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.send { color:#77bb77; }
.server { color:#7799bb; }
.error { color:#AA0000; }</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="bloop_markdown"><p>I haven’t followed the topic and while reading the proposal I found it a little confusing that we have inconsistent type names. I’m not a native English speaker so that’s might be the main case for my confusion here, so I’d appreciate for any clarification. ;-)</p>
<ul>
<li><p><code>SubSequence</code> vs. <code>Substring</code> and not <code>SubString</code>.</p></li>
<li><p>The word <code>substring</code> is an English word, but so is <code>subsequence</code> (I double checked here).</p></li>
</ul>
<p>So where exactly is the issue here? Is it <code>SubSequence</code> which is written in camel case or is it <code>Substring</code> which is not?</p>
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <br> <div id="bloop_sign_1490868971831119104" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div> <br><p class="airmail_on">Am 30. März 2017 um 02:32:39, Ben Cohen via swift-evolution (<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div></div><div>
<title></title>
Hi Swift Evolution,
<div class=""><br class=""></div>
<div class="">Below is a pitch for the first part of the String
revision. This covers a number of changes that would allow the
basic internals to be overhauled.</div>
<div class=""><br class=""></div>
<div class="">Online version here: <a href="https://github.com/airspeedswift/swift-evolution/blob/3a822c799011ace682712532cfabfe32e9203fbb/proposals/0161-StringRevision1.md" class="">https://github.com/airspeedswift/swift-evolution/blob/3a822c799011ace682712532cfabfe32e9203fbb/proposals/0161-StringRevision1.md</a></div>
<div class=""><br class=""></div>
<div class=""><br class=""></div>
<div class="">
<h1 id="string-revision-collection-conformance--c-interop--transcoding" data-orig-id="string-revision:-collection-conformance--c-interop--transcoding" style="box-sizing: border-box; font-size: 2.25em; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.2; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class="">String Revision: Collection Conformance, C Interop,
Transcoding</h1>
<ul style="box-sizing: border-box; padding: 0px 0px 0px 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">
<li style="box-sizing: border-box;" class="">
Proposal: <a href="file:///Users/ben_cohen/Documents/swift-evolution/proposals/0161-StringRevision1.md" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">SE-0161</a></li>
<li style="box-sizing: border-box;" class="">Authors: <a href="https://github.com/airspeedswift" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">Ben Cohen</a>, <a href="http://github.com/dabrahams/" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">Dave Abrahams</a></li>
<li style="box-sizing: border-box;" class="">Review Manager:
TBD</li>
<li style="box-sizing: border-box;" class="">
Status: <strong style="box-sizing: border-box;" class="">Awaiting review</strong></li>
</ul>
<h2 id="introduction" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Introduction</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">This proposal is to implement a subset of the changes from
the <a href="https://github.com/apple/swift/blob/master/docs/StringManifesto.md" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">Swift 4 String Manifesto</a>.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Specifically:</p>
<ul style="box-sizing: border-box; padding: 0px 0px 0px 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">
<li style="box-sizing: border-box;" class="">Make <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> conform to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">BidirectionalCollection</code></li>
<li style="box-sizing: border-box;" class="">Make <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> conform to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">RangeReplaceableCollection</code></li>
<li style="box-sizing: border-box;" class="">Create
a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> type for <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String.SubSequence</code></li>
<li style="box-sizing: border-box;" class="">Create
a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Unicode</code> protocol to allow for generic
operations over both types.</li>
<li style="box-sizing: border-box;" class="">Consolidate on a
concise set of C interop methods.</li>
<li style="box-sizing: border-box;" class=""><ins id="firstdiff" style="box-sizing: border-box; display: inline-block; position: absolute; left: -8px; text-decoration: none !important; border: none !important; background-image: none !important; background-position: initial initial !important; background-repeat: initial initial !important;" class=""></ins>Revise the transcoding infrastructure.</li>
</ul>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Other existing aspects of <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> remain unchanged for the purposes of
this proposal.</p>
<h2 id="motivation" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Motivation</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">This proposal follows up on a number of recommendations
found in the manifesto:</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class=""><code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Collection</code> conformance was dropped
from <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> in Swift 2. After reevaluation, the
feeling is that the minor semantic discrepancies (mainly
with <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">RangeReplaceableCollection</code>) are outweighed by the
significant benefits of restoring these conformances. For more
detail on the reasoning, see <a href="https://github.com/apple/swift/blob/master/docs/StringManifesto.md#string-should-be-a-collection-of-characters-again" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">here</a></p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">While it is not a collection, the Swift 3 string does have
slicing operations. <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> is currently serving as its own
subsequence, allowing substrings to share storage with their
“owner”. This can lead to memory leaks when small substrings of
larger strings are stored long-term (see <a href="https://github.com/apple/swift/blob/master/docs/StringManifesto.md#substrings" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">here</a> for more detail on this problem).
Introducing a separate type of <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> to serve as <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String.Subsequence</code> is recommended to resolve
this issue, in a similar fashion to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">ArraySlice</code>.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">As noted in the manifesto, support for interoperation with
nul-terminated C strings in Swift 3 is scattered and incoherent,
with 6 ways to transform a C string into a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> and four ways to do the inverse. These
APIs should be replaced with a simpler set of methods
on <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code>.</p>
<h2 id="proposed-solution" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Proposed solution</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">A new type, <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code>, will be introduced. Similar
to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">ArraySlice</code> it will be documented as only for
short- to medium-term storage:</p>
<blockquote style="box-sizing: border-box; margin: 0px 0px 16px; padding: 0px 15px; color: rgb(119, 119, 119); border-left-width: 4px; border-left-style: solid; border-left-color: rgb(221, 221, 221); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">
<p style="box-sizing: border-box; margin: 0px 0px 16px;" class="">
<strong style="box-sizing: border-box;" class="">Important</strong></p>
<div style="box-sizing: border-box; margin: 0px;" class="">
Long-term storage of <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> instances is discouraged. A
substring holds a reference to the entire storage of a larger
string, not just to the portion it presents, even after the
original string’s lifetime ends. Long-term storage of a substring
may therefore prolong the lifetime of elements that are no longer
otherwise accessible, which can appear to be memory leakage.</div>
</blockquote>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Aside from minor differences, such as having
a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">SubSequence</code> of <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Self</code> and a larger size to describe the range
of the subsequence, <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> will be near-identical from a user
perspective.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">In order to be able to write extensions accross
both <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> and <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code>, a new <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Unicode</code> protocol to which the two types will
conform will be introduced. For the purposes of this
proposal, <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Unicode</code> will be defined as a protocol to be
used whenver you would previously extend <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code>. It should be possible to
substitute <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">extension Unicode { ... }</code> in Swift 4
wherever <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">extension String { ... }</code> was written in Swift
3, with one exception: any passing of <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">self</code> into an API that takes a
concrete <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> will need to be rewritten
as <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String(self)</code>. If <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Self</code> is a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> then this should effectively optimize
to a no-op, whereas if <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Self</code> is a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> then this will force a copy, helping
to avoid the “memory leak” problems described above.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The exact nature of the protocol – such as which methods
should be protocol requirements vs which can be implemented as
protocol extensions, are considered implementation details and so
not covered in this proposal.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class=""><code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Unicode</code> will conform to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">BidirectionalCollection</code>. <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">RangeReplaceableCollection</code> conformance will be
added directly onto the <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> and <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> types, as it is possible
future <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Unicode</code>-conforming types might not be
range-replaceable (e.g. an immutable type that wraps
a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">const char *</code>).</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The C string interop methods will be updated to those
described <a href="https://github.com/apple/swift/blob/master/docs/StringManifesto.md#c-string-interop" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">here</a>: a single <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">withCString</code> operation and
two <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">init(cString:)</code> constructors, one for UTF8 and
one for arbitrary encodings. The primary change is to remove
“non-repairing” variants of construction from nul-terminated C
strings. In both of the construction APIs, any invalid encoding
sequence detected will have its longest valid prefix replaced
by <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">U+FFFD</code>, the Unicode replacement character, per the
Unicode specification. This covers the common case. The replacement
is done physically in the underlying storage and the validity of
the result is recorded in the String’s encoding such that future
accesses need not be slowed down by possible error repair
separately. Construction that is aborted when encoding errors are
detected can be accomplished using APIs on the encoding.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The current transcoding support will be updated to improve
usability and performance. The primary changes will be:</p>
<ul style="box-sizing: border-box; padding: 0px 0px 0px 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">
<li style="box-sizing: border-box;" class="">to allow transcoding
directly from one encoding to another without having to triangulate
through an intermediate scalar value</li>
<li style="box-sizing: border-box;" class="">to add the ability to
transcode an input collection in reverse, allowing the different
views on <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> to be made bi-directional</li>
<li style="box-sizing: border-box;" class="">to have decoding take
a collection rather than an iterator, and return an index of its
progress into the source, allowing that method to be static</li>
</ul>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The standard library currently lacks a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Latin1</code> codec, so a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">enum Latin1: UnicodeEncoding</code> type will be
added.</p>
<h2 id="detailed-design" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Detailed design</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The following additions will be made to the standard
library:</p>
<pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; margin-top: 0px; margin-bottom: 16px; font-stretch: normal; line-height: 1.45; padding: 16px; background-color: rgb(248, 248, 248); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; tab-size: 4; color: rgb(51, 51, 51); height: 248px;" class=""><code class="swift hljs" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; padding: 0.5em; margin: 0px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; border: 0px; display: block; overflow-x: auto; line-height: inherit; word-wrap: normal; height: auto;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">protocol</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Unicode</span>: <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">BidirectionalCollection</span> </span>{
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">// Implementation detail as described above</span>
}
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">extension</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span>: <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Unicode</span>, <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">RangeReplaceableCollection</span> </span>{
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">typealias</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span> = <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Substring</span>
}
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">struct</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Substring</span>: <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Unicode</span>, <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">RangeReplaceableCollection</span> </span>{
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">typealias</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span> = <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Substring</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">// near-identical API surface area to String</span>
}</code></pre>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The subscript operations on <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> will be amended to
return <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code>:</p>
<pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; margin-top: 0px; margin-bottom: 16px; font-stretch: normal; line-height: 1.45; padding: 16px; background-color: rgb(248, 248, 248); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; tab-size: 4; color: rgb(51, 51, 51); height: 112px;" class=""><code class="swift hljs" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; padding: 0.5em; margin: 0px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; border: 0px; display: block; overflow-x: auto; line-height: inherit; word-wrap: normal; height: auto;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">struct</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span> </span>{
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">subscript</span>(bounds: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Range</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>>) -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Substring</span> { <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">get</span> }
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">subscript</span>(bounds: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">ClosedRange</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>>) -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Substring</span> { <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">get</span> }
}</code></pre>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Note that properties or methods that due to their nature
create new <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> storage (such as <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">lowercased()</code>) will <em style="box-sizing: border-box;" class="">not</em> change.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">C string interop will be consolidated on the following
methods:</p>
<pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; margin-top: 0px; margin-bottom: 16px; font-stretch: normal; line-height: 1.45; padding: 16px; background-color: rgb(248, 248, 248); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; tab-size: 4; color: rgb(51, 51, 51); height: 418px;" class=""><code class="swift hljs" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; padding: 0.5em; margin: 0px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; border: 0px; display: block; overflow-x: auto; line-height: inherit; word-wrap: normal; height: auto;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">extension</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span> </span>{
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Constructs a `String` having the same contents as `nulTerminatedUTF8`.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">///</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// - Parameter nulTerminatedUTF8: a sequence of contiguous UTF-8 encoded </span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// bytes ending just before the first zero byte (NUL character).</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">init</span>(cString nulTerminatedUTF8: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">UnsafePointer</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">CChar</span>>)
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Constructs a `String` having the same contents as `nulTerminatedCodeUnits`.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">///</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// - Parameter nulTerminatedCodeUnits: a sequence of contiguous code units in</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// the given `encoding`, ending just before the first zero code unit.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// - Parameter encoding: describes the encoding in which the code units</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// should be interpreted.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">init</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Encoding</span>: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">UnicodeEncoding</span>>(
cString nulTerminatedCodeUnits: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">UnsafePointer</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Encoding</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">CodeUnit</span>>,
encoding: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Encoding</span>)
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Invokes the given closure on the contents of the string, represented as a</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// pointer to a null-terminated sequence of UTF-8 code units.</span>
<span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">func</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(153, 0, 0); font-weight: bold;">withCString</span><Result><span class="hljs-params" style="box-sizing: border-box;">(
<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span> body: <span class="hljs-params" style="box-sizing: border-box;">(UnsafePointer<CChar>)</span></span></span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">throws</span> -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Result</span>) <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">rethrows</span> -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Result</span>
}</code></pre>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Additionally, the current ability to pass a
Swift <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> into C methods that take a C string
will remain as-is.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">A new protocol, <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">UnicodeEncoding</code>, will be added to replace the
current <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">UnicodeCodec</code> protocol:</p>
<pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; margin-top: 0px; margin-bottom: 16px; font-stretch: normal; line-height: 1.45; padding: 16px; background-color: rgb(248, 248, 248); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; tab-size: 4; color: rgb(51, 51, 51); height: 1353px;" class=""><code class="swift hljs" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; padding: 0.5em; margin: 0px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; border: 0px; display: block; overflow-x: auto; line-height: inherit; word-wrap: normal; height: auto;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">enum</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">UnicodeParseResult</span><<span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">T</span>, <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>> </span>{
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Indicates valid input was recognized.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">///</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// `resumptionPoint` is the end of the parsed region</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">case</span> valid(<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">T</span>, resumptionPoint: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>) <span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">// <span class="hljs-doctag" style="box-sizing: border-box; color: rgb(221, 17, 68);">FIXME:</span> should these be reordered?</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Indicates invalid input was recognized.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">///</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// `resumptionPoint` is the next position at which to continue parsing after</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// the invalid input is repaired.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">case</span> error(resumptionPoint: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>)
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Indicates that there was no more input to consume.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">case</span> emptyInput
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// If any input was consumed, the point from which to continue parsing.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">var</span> resumptionPoint: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>? {
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">switch</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">self</span> {
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">case</span> .valid(<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span>,<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">let</span> r): <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">return</span> r
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">case</span> .error(<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">let</span> r): <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">return</span> r
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">case</span> .emptyInput: <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">return</span> <span class="hljs-literal" style="box-sizing: border-box; color: rgb(0, 128, 128);">nil</span>
}
}
}
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// An encoding for text with UnicodeScalar as a common currency type</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">protocol</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">UnicodeEncoding</span> </span>{
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// The maximum number of code units in an encoded unicode scalar value</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">var</span> maxLengthOfEncodedScalar: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Int</span> { <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">get</span> }
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// A type that can represent a single UnicodeScalar as it is encoded in this</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// encoding.</span>
associatedtype <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span> : <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalarProtocol</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Produces a scalar of this encoding if possible; returns `nil` otherwise.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">func</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(153, 0, 0); font-weight: bold;">encode</span><Scalar: EncodedScalarProtocol><span class="hljs-params" style="box-sizing: border-box;">(
<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span>:Scalar)</span></span> -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Self</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span>?
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Parse a single unicode scalar forward from `input`.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">///</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// - Parameter knownCount: a number of code units known to exist in `input`.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// **Note:** passing a known compile-time constant is strongly advised,</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// even if it's zero.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">func</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(153, 0, 0); font-weight: bold;">parseScalarForward</span><C: Collection><span class="hljs-params" style="box-sizing: border-box;">(
<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span> input: C, knownCount: Int <span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/* = 0, via extension */</span>
)</span></span> -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">ParseResult</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span>, <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">where</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Iterator</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Element</span> == <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Iterator</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Element</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Parse a single unicode scalar in reverse from `input`.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">///</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// - Parameter knownCount: a number of code units known to exist in `input`.</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// **Note:** passing a known compile-time constant is strongly advised,</span>
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// even if it's zero.</span>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">func</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(153, 0, 0); font-weight: bold;">parseScalarReverse</span><C: BidirectionalCollection><span class="hljs-params" style="box-sizing: border-box;">(
<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span> input: C, knownCount: Int <span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/* = 0 , via extension */</span>
)</span></span> -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">ParseResult</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span>, <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>>
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">where</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Iterator</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Element</span> == <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Iterator</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Element</span>
}
<span class="hljs-comment" style="box-sizing: border-box; color: rgb(153, 153, 136); font-style: italic;">/// Parsing multiple unicode scalar values</span>
<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">extension</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">UnicodeEncoding</span> </span>{
@discardableResult
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">public</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">func</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(153, 0, 0); font-weight: bold;">parseForward</span><C: Collection><span class="hljs-params" style="box-sizing: border-box;">(
<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span> input: C,
repairingIllFormedSequences makeRepairs: Bool = <span class="hljs-literal" style="box-sizing: border-box; color: rgb(0, 128, 128);">true</span>,
into output: <span class="hljs-params" style="box-sizing: border-box;">(EncodedScalar)</span></span></span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">throws</span>-><span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Void</span>
) <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">rethrows</span> -> (remainder: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span>, errorCount: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Int</span>)
@discardableResult
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">public</span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">static</span> <span class="hljs-function" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">func</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(153, 0, 0); font-weight: bold;">parseReverse</span><C: BidirectionalCollection><span class="hljs-params" style="box-sizing: border-box;">(
<span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">_</span> input: C,
repairingIllFormedSequences makeRepairs: Bool = <span class="hljs-literal" style="box-sizing: border-box; color: rgb(0, 128, 128);">true</span>,
into output: <span class="hljs-params" style="box-sizing: border-box;">(EncodedScalar)</span></span></span> <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">throws</span>-><span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Void</span>
) <span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">rethrows</span> -> (remainder: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span>, errorCount: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Int</span>)
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">where</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span> : <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">BidirectionalCollection</span>,
<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span> == <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span>,
<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">C</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">SubSequence</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Iterator</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Element</span> == <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">EncodedScalar</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Iterator</span>.<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Element</span>
}</code></pre>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class=""><code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">UnicodeCodec</code> will be updated to
refine <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">UnicodeEncoding</code>, and all existing codecs will
conform to it.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Note, depending on whether this change lands before or
after some of the generics features, generic <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">where</code> clauses may need to be added
temporarily.</p>
<h2 id="source-compatibility" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Source compatibility</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Adding collection conformance to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> should not materially impact source
stability as it is purely additive: Swift 3’s <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> interface currently fulfills all of the
requirements for a bidirectional range replaceable collection.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Altering <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code>’s slicing operations to return a different
type is source breaking. The following mitigating steps are
proposed:</p>
<ul style="box-sizing: border-box; padding: 0px 0px 0px 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">
<li style="box-sizing: border-box;" class="">
<p style="box-sizing: border-box; margin: 16px 0px;" class="">Add a
deprecated subscript operator that will run in Swift 3
compatibility mode and which will return a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> not a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code>.</p>
</li>
<li style="box-sizing: border-box;" class="">
<p style="box-sizing: border-box; margin: 16px 0px;" class="">Add
deprecated versions of all current slicing methods to similarly
return a <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code>.</p>
</li>
</ul>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">i.e.:</p>
<pre style="box-sizing: border-box; overflow: auto; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; margin-top: 0px; margin-bottom: 16px; font-stretch: normal; line-height: 1.45; padding: 16px; background-color: rgb(248, 248, 248); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; tab-size: 4; color: rgb(51, 51, 51); height: 231px;" class=""><code class="swift hljs" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; padding: 0.5em; margin: 0px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; border: 0px; display: block; overflow-x: auto; line-height: inherit; word-wrap: normal; height: auto;"><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">extension</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span> </span>{
<span class="hljs-meta" style="box-sizing: border-box; color: rgb(153, 153, 153); font-weight: bold;">@available</span>(swift, obsoleted: <span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">4</span>)
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">subscript</span>(bounds: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Range</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>>) -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span> {
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">return</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span>(characters[bounds])
}
<span class="hljs-meta" style="box-sizing: border-box; color: rgb(153, 153, 153); font-weight: bold;">@available</span>(swift, obsoleted: <span class="hljs-number" style="box-sizing: border-box; color: rgb(0, 128, 128);">4</span>)
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">subscript</span>(bounds: <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">ClosedRange</span><<span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">Index</span>>) -> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span> {
<span class="hljs-keyword" style="box-sizing: border-box; font-weight: bold;">return</span> <span class="hljs-type" style="box-sizing: border-box; color: rgb(68, 85, 136); font-weight: bold;">String</span>(characters[bounds])
}
}</code></pre>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">In a review of 77 popular Swift projects found on GitHub,
these changes resolved any build issues in the 12 projects that
assumed an explicit <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> type returned from slicing
operations.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Due to the change in internal implementation, this means
that these operations will be <em style="box-sizing: border-box;" class="">O(n)</em> rather
than <em style="box-sizing: border-box;" class="">O(1)</em>.
This is not expected to be a major concern, based on experiences
from a similar change made to Java, but projects will be able to
work around performance issues without upgrading to Swift 4 by
explicitly typing slices as <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code>, which will call the Swift 4 variant, and
which will be available but not invoked by default in Swift 3
mode.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">The C string interoperability methods outside the ones
described in the detailed design will remain in Swift 3 mode, be
deprecated in Swift 4 mode, and be removed in a subsequent
release. <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">UnicodeCodec</code> will be similarly deprecated.</p>
<h2 id="effect-on-abi-stability" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Effect on ABI stability</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">As a fundamental currency type for Swift, it is essential
that the <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> type (and its associated subsequence)
is in a good long-term state before being locked down when Swift
declares ABI stability. Shrinking the size of <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> to be 64 bits is an important part of
this.</p>
<h2 id="effect-on-api-resilience" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Effect on API resilience</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">Decisions about the API resilience of
the <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> type are still to be determined, but
are not adversely affected by this proposal.</p>
<h2 id="alternatives-considered" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; position: relative; color: rgb(51, 51, 51); padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); font-family: helvetica, arial, freesans, clean, sans-serif; background-color: rgb(255, 255, 255);" class="">Alternatives considered</h2>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">For a more in-depth discussion of some of the trade-offs
in string design, see the manifesto and associated <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170116/thread.html#30497" style="box-sizing: border-box; background-color: transparent; color: rgb(65, 131, 196); text-decoration: none;" class="">evolution thread</a>.</p>
<p style="box-sizing: border-box; margin: 0px 0px 16px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255);" class="">This proposal does not yet introduce an implicit
conversion from <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Substring</code> to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code>. The decision on whether to add this will be
deferred pending feedback on the initial implementation. The
intention is to make a preview toolchain available for feedback,
including on whether this implicit conversion is necessary, prior
to the release of Swift 4.</p>
<div style="box-sizing: border-box; margin-top: 0px; margin-right: 0px; margin-left: 0px; color: rgb(51, 51, 51); font-family: helvetica, arial, freesans, clean, sans-serif; font-size: 12.799999237060547px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;" class="">Several of the types related to <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code>, such as the encodings, would ideally reside
inside a namespace rather than live at the top level of the
standard library. The best namespace for this is
probably <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">Unicode</code>, but this is also the name of the protocol.
At some point if we gain the ability to nest enums and types inside
protocols, they should be moved there. Putting them
inside <code style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 10.880000114440918px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;" class="">String</code> or some other enum namespace is
probably not worthwhile in the mean-time.</div>
</div>
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