[swift-evolution] [swift-evolution-announce] [Review] SE-0027 Expose code unit initializers on String

Kevin Ballard kevin at sb.org
Tue Feb 16 23:15:09 CST 2016

I'm very much a fan of the end result of this proposal, i.e. some way to
convert from a collection of code units into a String. Initially I
thought the proposed API was acceptable, barring some quibbles about
naming, but I think Dave Abrahams has made some good points in this
thread, and so I'll just say that I very much support getting this kind
of functionality in the stdlib, but if Dave Abrahams thinks that the API
as proposed isn't what we want in the long term, then I'll defer to his

Also, given the proposed API, the input really should be a SequenceType.
I recognize that it's calling through to _StringBuffer.fromCodeUnits()
which takes a CollectionType, but the only reason that takes a
CollectionType is so it can pre-calculate the size of the UTF-16 buffer,
and I don't think that limitation should be exposed through the public
API. It would be better to change _StringBuffer.fromCodeUnits() to take
a SequenceType and use the _preprocessingPass machinery to choose
between the fast-path of pre-allocating the buffer and a slow path of
growing the buffer as needed.

-Kevin Ballard

On Thu, Feb 11, 2016, at 04:41 PM, Douglas Gregor wrote:
> Hello Swift community,

> The review of SE-0027 "Expose code unit initializers on String"
> begins now and runs through February 16, 2016. The proposal is
> available here:

>> https://github.com/apple/swift-evolution/blob/master/proposals/0027-string-from-code-units.md
> Reviews are an important part of the Swift evolution process. All
> reviews should be sent to the swift-evolution mailing list at

>> https://lists.swift.org/mailman/listinfo/swift-evolution
> or, if you would like to keep your feedback private, directly to the
> review manager. When replying, please try to keep the proposal link at
> the top of the message:

>> Proposal link:

>>> https://github.com/apple/swift-evolution/blob/master/proposals/0027-string-from-code-units.md
>> Reply text

>>> Other replies
> What goes into a review?

> The goal of the review process is to improve the proposal under review
> through constructive criticism and, eventually, determine the
> direction of Swift. When writing your review, here are some questions
> you might want to answer in your review:

>  * What is your evaluation of the proposal?
>  * Is the problem being addressed significant enough to warrant a
>    change to Swift?
>  * Does this proposal fit well with the feel and direction of Swift?
>  * If you have used other languages or libraries with a similar
>    feature, how do you feel that this proposal compares to those?
>  * How much effort did you put into your review? A glance, a quick
>    reading, or an in-depth study? More information about the Swift
>    evolution process is available at

>> https://github.com/apple/swift-evolution/blob/master/process.md
> Thank you,

> Doug Gregor

> Review Manager

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