[swift-evolution] [Review] SE-0168: Multi-Line String Literals

John Holdsworth mac at johnholdsworth.com
Sun Apr 9 11:29:49 CDT 2017

Hi, John here, the submitter of the proposal.

First up, I must apologise for putting Brent on the spot when I resubmitted this altered proposal from last year. That was my mistake.

Second up, apologies if the proposal is rather vague on details. In some sense this was intentional as I didn’t want to get too bogged down in specifics (and not at all to do with my limitations as a technical writer!)

I guess we need to build up consensus more slowly by asking the following questions separately so it can be resubmitted rather than giving a binary +/-1 on the proposal as it stands.

1) Does Swift need multi-line string literals?
2 ) Is “””long strings””” the way to go subject to a discussion about the precise delimiter
3) Is the “magic" leading whitespace removal a good idea to support indentation.
4) Does the proposal contain sufficient detail to be discussed/implemented

My answer to 1) is obviously yes and I think the discussion has come out about 50/50 so far so lets persevere...

Trying to fie down 2), a “””long string””” or @“long string”@ or _”long string”_ or #”long string”# is a string literal inside a new delimiter. It would be processed exactly as it would a normal string including escapes and interpolation except the string can include unescaped “ or  “" and newlines. Also, a \ at the end of the line would mean that particular newline is not included in the string.

For me, the goals of a long string are that it should be able to pasted in (almost) without modification from a text source and that syntax highlighting would work for the widest possible range of text editors and github. “””long string””” is just a trick Python uses to satisfy the second goal (for example this gist <https://gist.github.com/johnno1962/5c325a16838ad3c73e0f109a514298bf#file-multiline-swift-L97>) but highlighting also works for asymmetric delimiters such as @“long string”@ which avoid potential problems with “inversion”. Heredoc or a Swifty #equivalent does not satisfy this second goal at all well and IMHO it should be excluded. It would also be significantly more difficult to integrate into the Swift compiler.

Looking at 3) which is underspecified in the proposal perhaps, I’d consider it a “feature" but I can see it would be too magical for some. To specify it more you could say: if there is only whitespace between the last newline and the end of a multiline literal this whitespace will be stripped from all lines in the literal. If lines do not start with this exact sequence of whitespace a warning is emitted. In addition, if the first character in the literal is a newline it will be removed. This operation could be made explicit e.g. #trimLeft(“”"a literal""")

Perhaps we can find common ground on 1) and 2) and even 3) with a view to resubmitting if there is time. Seems mostly like we just need to discuss the delimiter further and decide whether the indent trimming is a bug or a feature to keep moving and not let another year slip by.

With respect to 4) I’m updating https://github.com/johnno1962a/swift-evolution/blob/master/proposals/0168-multi-line-string-literals.md <https://github.com/johnno1962a/swift-evolution/blob/master/proposals/0168-multi-line-string-literals.md> as the proposal is discussed to fill in some of the gaps & I’ve prepared a toolchain for Swift 3 if you want to try an implementation out  <http://johnholdsworth.com/swift-LOCAL-2017-04-09-a-osx.tar.gz>

> On 9 Apr 2017, at 15:35, Thorsten Seitz via swift-evolution <swift-evolution at swift.org> wrote:
>> https://github.com/apple/swift-evolution/blob/master/proposals/0168-multi-line-string-literals.md <https://github.com/apple/swift-evolution/blob/master/proposals/0168-multi-line-string-literals.md>
>> What is your evaluation of the proposal?
> +1
> My foremost expectation from multiline string literals is to be able to copy and paste multiline string literals without having to fiddle with escape marks or leading and trailing quotes or continuation characters. This is exactly what the proposal provides and makes it easy to embed SQL, for example (using SQL parameters and not string interpolation of course ;-)
> The chosen deindentation rules seem very pragmatic and useful to me.
> Additional features for multiline string literals can be added easily later.
> I would expect multiline string literals to use the same newline character as "\n“ does, regardless of the newline character actually used in the file.
> Furthermore all normal escapes, e.g. \n, \t etc. should probably be available as well. 
> This should be stated explicitly in the proposal.
>> Is the problem being addressed significant enough to warrant a change to Swift?
> Yes.
>> Does this proposal fit well with the feel and direction of Swift?
> Yes.
>> If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> For setting the ground it compares favourably.
>> How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> Followed most discussions, read the proposal.
> -Thorsten
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