<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Hi Chris,<div class=""><br class=""></div><div class="">Thank you for the feedback; it is much appreciated.</div><div class=""><br class=""></div><div class="">I like the idea of folding this into the language's pattern grammar. It makes it more Swifty. I didn't see that direction, and I will investigate it further.</div><div class=""><br class=""></div><div class="">I have been looking a lot at Perl 6. In fact, a lot of languages these days use PCRE or PCRE2, which was based on Perl's implementation of regular expressions. Does this mean there is attitude to move away from the regular expression implementation used by the foundation today?</div><div class=""><br class=""></div><div class="">Cheers,</div><div class="">-Patrick</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jan 31, 2016, at 10:39 PM, Chris Lattner <<a href="mailto:clattner@apple.com" class="">clattner@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><br class="Apple-interchange-newline">On Jan 31, 2016, at 8:32 AM, Patrick Gili via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">There have been several threads that have discussed the notion of a regular expression literals. However, I didn't see anyone putting together a formal proposal, and hence I took the liberty to do so. I would appreciate discussion and comments on the proposal:</div></div></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">I am +1 on the concept of adding regex literals to Swift, but -1 on this proposal.</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Specifically, instead of introducing regex literals, I’d suggest that you investigate introducing regex’s to the pattern grammar, which is what Swift uses for matching already. Regex’s should be usable in the cases of a switch, for example. Similarly, they should be able to bind variables directly to subpatterns.</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Further, I highly recommend checking out Perl 6’s regular expressions. They are a community that has had an obsessive passion for regular expressions, and in Perl 6 they were given the chance to reinvent the wheel based on what they learned. What they came up with is very powerful, and pretty good all around.</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">-Chris</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><br class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><blockquote type="cite" class="" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><br class=""></div><div class=""><h1 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 28px; font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Regular Expression Literals</h1><ul class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; padding-left: 30px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">Proposal: [SE-NNNN] (<a href="https://github/apple/swift-evolution/blob/master/proposals/NNNN-name.md" class="">https://github/apple/swift-evolution/blob/master/proposals/NNNN-name.md</a>)</li><li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">Author: Patrick Gili (<a href="https://github.com/gili-patrick-r" class="">https://github.com/gili-patrick-r</a>)</li><li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">Status: <strong class="" style="-webkit-print-color-adjust: exact; margin-top: 0px;">Awaiting review</strong></li><li class="" style="-webkit-print-color-adjust: exact; margin: 0px;">Review manager: TBD</li></ul><h2 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 24px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(204, 204, 204); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Introduction</h2><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The Swift language has no native support for regular expressions, which makes working with regular expressions in Swift awkward, tedious, and error prone. This proposal describes the addition of regular expressions literals to Swift.</p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">Swift-evolution thread: <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151228/005126.html" class="" style="-webkit-print-color-adjust: exact; color: rgb(65, 131, 196);">Empower String type with regular expression</a></p><h2 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 24px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(204, 204, 204); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Motivation</h2><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The definition of a pattern used by a regular expression is complicated by the fact that Swift does not support raw string literals (i.e., string literals that do not process character escapes or interpolation) or regular expression literals similar to Perl or Ruby. Rather, Swift only supports C-style string literals with support for interpolation. C-style string literals require a backslash to escape a backslash. The patterns representing regular expressions make frequent use of the backslash, and hence patterns represented by a Swift string literal become unreadable and difficult to maintain. For example, consider the following pattern to match and parse URLs:</p><pre class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-bottom: 15px; background-color: rgb(248, 248, 248); border: 1px solid rgb(204, 204, 204); font-size: 13px; line-height: 19px; overflow: auto; padding: 6px 10px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;"><code class="" style="-webkit-print-color-adjust: exact; margin: 0px; padding: 0px; border: none; background-color: transparent; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$
</code></pre><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">To define this pattern in Swift, an application needs to define a string, such as</p><pre class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-bottom: 15px; background-color: rgb(248, 248, 248); border: 1px solid rgb(204, 204, 204); font-size: 13px; line-height: 19px; overflow: auto; padding: 6px 10px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;"><code class="" style="-webkit-print-color-adjust: exact; margin: 0px; padding: 0px; border: none; background-color: transparent; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">let pattern = "^(https?:\\/\\/)?([\\da-z\\.-]+)\\.([a-z\\.]{2,6})([<a href="smb://///w" class="">\\/\\w</a> <a href="smb://.-" class="">\\.-</a>]*)*\\/?$"
</code></pre><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">This later is obviously difficult to read and maintain.</p><h2 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 24px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(204, 204, 204); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Proposed solution</h2><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The proposed solution is to add regular expression literals to Swift, similar to regular expression literal support by other languages, such as Perl and Ruby. Regular expression literals differ from raw string literals in two primary ways. First, regular expression literals support string interpolation of the pattern, which allows an application to construct a regular expression at run-time. Second, a regular expression literal creates an instance of a NSRegularExpression, rather than an instance of String. The following example declares a regular expression for the purpose of matching and parsing URIs with a specified scheme:</p><pre class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-bottom: 15px; background-color: rgb(248, 248, 248); border: 1px solid rgb(204, 204, 204); font-size: 13px; line-height: 19px; overflow: auto; padding: 6px 10px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;"><code class="" style="-webkit-print-color-adjust: exact; margin: 0px; padding: 0px; border: none; background-color: transparent; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">let scheme = "https"
let urlRegex = /^(\(scheme)?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/
</code></pre><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">To make regular expression literals effective, it must be possible to replace the creation of any instance of NSRegularExpression. The initializer for NSRegularExpression accepts a string describing the pattern and a set of options. To support these options, a regular expression literal accepts a list of zero or more options after the delimiter closing the pattern. For example, consider a regular expression to match and parse email addresses.</p><pre class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-bottom: 15px; background-color: rgb(248, 248, 248); border: 1px solid rgb(204, 204, 204); font-size: 13px; line-height: 19px; overflow: auto; padding: 6px 10px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;"><code class="" style="-webkit-print-color-adjust: exact; margin: 0px; padding: 0px; border: none; background-color: transparent; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">let emailRegex = /^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/
</code></pre><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">This regular expression will match "<a href="mailto:john.appleseed@apple.com" class="">john.appleseed@apple.com</a>"", but not "<a href="mailto:JOHN.APPLESEED@apple.com" class="">JOHN.APPLESEED@APPLE.COM</a>". The regular expression has to allow for this, as email addresses are not case sensitive. Rather than add the complexity to the pattern to account for this, the following example achieves the same:</p><pre class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-bottom: 15px; background-color: rgb(248, 248, 248); border: 1px solid rgb(204, 204, 204); font-size: 13px; line-height: 19px; overflow: auto; padding: 6px 10px; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;"><code class="" style="-webkit-print-color-adjust: exact; margin: 0px; padding: 0px; border: none; background-color: transparent; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">let emailRegex = /^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/i
</code></pre><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">In this case, the "i" following the delimiter closing the pattern maps to RegularExpressionOption.CaseInsensitive.</p><h2 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 24px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(204, 204, 204); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Detailed design</h2><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The following modification to the grammar of a literal adds support for regular expression literals:</p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><em class="" style="-webkit-print-color-adjust: exact;">literal</em> → <em class="" style="-webkit-print-color-adjust: exact;">numeric-literal</em> | <em class="" style="-webkit-print-color-adjust: exact;">string-literal</em> | <em class="" style="-webkit-print-color-adjust: exact;">boolean-literal</em> | <em class="" style="-webkit-print-color-adjust: exact;">regex-literal</em> | <em class="" style="-webkit-print-color-adjust: exact;">nil-literal</em></p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The following grammar describes a regular expression literal:</p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><em class="" style="-webkit-print-color-adjust: exact;">regex-literal</em> → <em class="" style="-webkit-print-color-adjust: exact;">static-regex-literal</em> | <em class="" style="-webkit-print-color-adjust: exact;">interpolated-regex-literal</em></p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><em class="" style="-webkit-print-color-adjust: exact;">static-regex-literal</em> → / <em class="" style="-webkit-print-color-adjust: exact;">pattern</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub> / <em class="" style="-webkit-print-color-adjust: exact;">regex-options</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub><br class="" style="-webkit-print-color-adjust: exact;"><em class="" style="-webkit-print-color-adjust: exact;">pattern</em> → <em class="" style="-webkit-print-color-adjust: exact;">pattern_item</em> <em class="" style="-webkit-print-color-adjust: exact;">pattern</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub><br class="" style="-webkit-print-color-adjust: exact;"><em class="" style="-webkit-print-color-adjust: exact;">pattern_item</em> → any Unicode scalar value except /, U+000A, or U+000D</p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><em class="" style="-webkit-print-color-adjust: exact;">interpolated-string-literal</em> → / <em class="" style="-webkit-print-color-adjust: exact;">interpolated-pattern</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub> / <em class="" style="-webkit-print-color-adjust: exact;">regex-options</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub><br class="" style="-webkit-print-color-adjust: exact;"><em class="" style="-webkit-print-color-adjust: exact;">interpolated_pattern</em> → <em class="" style="-webkit-print-color-adjust: exact;">interpolated_pattern_item</em> <em class="" style="-webkit-print-color-adjust: exact;">interpolated_pattern</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub><br class="" style="-webkit-print-color-adjust: exact;"><em class="" style="-webkit-print-color-adjust: exact;">interpolated_pattern_item</em> → ( <em class="" style="-webkit-print-color-adjust: exact;">expression</em> ) | <em class="" style="-webkit-print-color-adjust: exact;">pattern_item</em></p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><em class="" style="-webkit-print-color-adjust: exact;">regex-options</em> → <em class="" style="-webkit-print-color-adjust: exact;">regex-option</em> | <em class="" style="-webkit-print-color-adjust: exact;">regex-option</em><sub class="" style="-webkit-print-color-adjust: exact;">opt</sub><br class="" style="-webkit-print-color-adjust: exact;"><em class="" style="-webkit-print-color-adjust: exact;">regex_option</em> → <strong class="" style="-webkit-print-color-adjust: exact;">i</strong> | <strong class="" style="-webkit-print-color-adjust: exact;">x</strong> | <strong class="" style="-webkit-print-color-adjust: exact;">q</strong> | <strong class="" style="-webkit-print-color-adjust: exact;">s</strong> | <strong class="" style="-webkit-print-color-adjust: exact;">m</strong> | <strong class="" style="-webkit-print-color-adjust: exact;">d</strong> | <strong class="" style="-webkit-print-color-adjust: exact;">b</strong></p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The following table summarize the regular expression options:</p><table class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; padding: 0px; border-collapse: collapse; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><thead class="" style="-webkit-print-color-adjust: exact;"><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); margin: 0px; padding: 0px;"><th class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">Option </th><th class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">RegularExpressionOption </th></tr></thead><tbody class="" style="-webkit-print-color-adjust: exact;"><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">i </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">CaseInsensitive </td></tr><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); background-color: rgb(248, 248, 248); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">x </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">AllowCommentsAndWhitespace </td></tr><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">q </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">IgnoreMetacharacters </td></tr><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); background-color: rgb(248, 248, 248); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">s </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">DotMatchesLineSeparations </td></tr><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">m </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">AnchorsMatchLines </td></tr><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); background-color: rgb(248, 248, 248); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">d </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">UseUnixLineSeparators </td></tr><tr class="" style="-webkit-print-color-adjust: exact; border-top-width: 1px; border-top-style: solid; border-top-color: rgb(204, 204, 204); margin: 0px; padding: 0px;"><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">b </td><td class="" style="-webkit-print-color-adjust: exact; border: 1px solid rgb(204, 204, 204); margin: 0px; padding: 6px 13px;">UseUnicodeWordBoundaries </td></tr></tbody></table><h2 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 24px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(204, 204, 204); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Impact on existing code</h2><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">The use of regular expression literals is opt-in, and hence there is no impact to existing code.</p><h2 class="" style="-webkit-print-color-adjust: exact; margin: 20px 0px 10px; padding: 0px; -webkit-font-smoothing: antialiased; cursor: text; position: relative; font-size: 24px; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(204, 204, 204); font-family: Helvetica, arial, sans-serif; background-color: rgb(255, 255, 255);">Alternatives considered</h2><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);">There have been several threads on the swift-evoluation mailing list that have discussed alternatives to regular expression literals.</p><p class="" style="-webkit-print-color-adjust: exact; margin: 15px 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255);"><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002193.html" class="" style="-webkit-print-color-adjust: exact; color: rgb(65, 131, 196);">String literal suffixes for defining types</a> discussed string literals with a single character appended after the closing delimiter to denote the type. For example, the string literal <code class="" style="-webkit-print-color-adjust: exact; margin: 0px 2px; padding: 0px 5px; white-space: nowrap; border: 1px solid rgb(234, 234, 234); 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;">r"\d+"</code> in Python denotes a regular expression literal. However, this approach suffers from two disadvantages: 1) it does not support string interpolation in the pattern, and 2) it uses double-quotes for the delimiter, which appears more frequently in regular expressions than the forward slash.</p><p class="" style="-webkit-print-color-adjust: exact; margin-top: 15px; margin-right: 0px; margin-left: 0px; font-family: Helvetica, arial, sans-serif; font-size: 14px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;"><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20151214/002325.html" class="" style="-webkit-print-color-adjust: exact; color: rgb(65, 131, 196);">Muli-line string literals</a> discussed string literals spanning more than one line. This would be a worthy addition to the regular expression literal discussed in this proposal. We should consider modifying the grammar to support this. However, I wanted to introduce changes incrementally to maintain focus.</p></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></div></blockquote></div></blockquote></div><br class=""></div></body></html>