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

Xiaodi Wu xiaodi.wu at gmail.com
Fri Apr 21 17:01:11 CDT 2017

On Fri, Apr 21, 2017 at 2:42 PM, Robert Bennett <rltbennett at icloud.com>

> It looks like we have different interpretations about what "literal" means
> (I think this may have been brought up in earlier messages in this thread;
> I don't remember the resolution). I interpreted it as meaning the same
> thing as literal in *LiteralConvertible, i.e., a Swift type that is written
> out in source. Multiline string literal would then refer to a multiline
> "piece of source code representing a String". It sounds like you are taking
> "literal" to mean something that *literally* (to the extent possible)
> represents its data, which in the case of String would mean writing out the
> source code exactly as the resulting String will appear. Up until now I
> think those two interpretations of "literal" were equivalent. For no type
> other than String is the physical layout in source related to the
> underlying data, and prior to this proposal the point was moot for String
> because there was only a single allowable layout (barring concatenation
> with +, which utilizes multiple independent literals).
> So, my view of the goal of this proposal is to allow writing a
> StringLiteralType across multiple lines. It appears your view is to allow
> using multiple lines to *literally* represent a String's content.

Yes, indeed, a very good summary. I think, if I read between the lines
correctly, the core team is intentionally making sure that these two views
of a literal will remain equivalent, based on which subset of the current
proposal has been accepted and which has been stricken. I'm arguing here
that we should continue down that road.

Again, for editors that indent wrapped lines, disallowing manually breaking
> lines will actually introduce ambiguity into the multiline string, which
> runs counter to the goal of the proposal. Also, from an ideological
> standpoint I see no reason to disallow this feature.

I'm not supremely opposed to it either. The point of this exercise is to
tease out what exactly is accomplished by adding it and whether it's worth
the implementation effort and additional complexity in features. Surely,
there is more to be said for it than merely accommodating people who don't
like the look of soft-wrapped text.

The other point of the exercise is to discuss how it impacts our
conceptions of what a literal is and what it ought to be.

On additional aim here is to drive home the point that escaping line breaks
is not an issue inherent to _multiline_ strings, but even single-line
strings might need to be broken up into multiple lines of source code. So,
if we agree that escaping newlines is a feature that we want to have, a
design that addresses """this""" but not "this" is incomplete and
needlessly restrictive.

One final aim is to argue that whether or not this feature is added, it is
an orthogonal question to that of trailing whitespace at the end of lines
in a multiline literal. For the moment, that is the most salient part of
the conversation, given the thread that we're in.

-- Robert
> On Apr 21, 2017, at 2:48 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> On Fri, Apr 21, 2017 at 1:45 PM, Erica Sadun <erica at ericasadun.com> wrote:
>> On Apr 21, 2017, at 12:40 PM, Xiaodi Wu via swift-evolution <
>> swift-evolution at swift.org> wrote:
>> On Fri, Apr 21, 2017 at 8:48 AM, Robert Bennett via swift-evolution <
>> swift-evolution at swift.org> wrote:
>>> Xiaodi, I think one thing you're neglecting is that users may never
>>> print out a multiline literal string at all. A string might never be
>>> printed or read by a human outside of the code it resides in. In this case
>>> it seems perfectly reasonable to ask that it be possible to format the
>>> string nicely in the code and disregard how it would actually be printed.
>> Can you give an example of such a use case, where a string is never seen
>> by a human but one cannot insert literal newlines and would need elided
>> ones instead?
>> The most common reason is that the code is maintained by a (non-human)
>> developer, who wants to be able to see and update the code in a readable
>> form, but that represents a single line that will automatically wrapped by,
>> for example, a UITextView for (human) consumption.
> A different scenario from what Robert's describing, but sure. This goes to
> my question to David Hart. Isn't this an argument for a feature to allow
> breaking a single-line string literal across multiple lines? What makes
> this a use case for some feature for _multiline_ string literals in
> particular?
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