[swift-evolution] [Pitch] Improve String Literals

Sat May 13 01:42:32 CDT 2017

> On 12 May 2017, at 23:14, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> 
> I feel like a broken record: Of the three proposed components of the proposed solution, two were amply considered by the community and the core team in SE-0168. The decision has already been made _not_ to implement these ideas at this time.

Can you provide me with quote from the Core Team that it should not be implemented at this time? I have troubles finding it.

> Significant defects discovered after the fact during implementation or new insights after extensive usage can prompt revisiting the decision, but that is not the case here: implementation did not require further clarification and the feature has only just landed on master. We simply cannot revisit topics willy-nilly. The process simply cannot work that way: few have the time and energy to offer their fullest consideration the first time round, and no one would be willing to do that if it means that the same topic will be revisited one month later.

The concerns summarised in this proposal were only heavily discussed after the acceptance of multi-line strings. Therefore, there is a great chance that they were not discussed by the Core Team. We feel obliged to put this proposal forward to formalise those issues.

If someone from the Core Team lets us know this is definitely out of scope for Swift 4, we’ll be happy to bring it back once discussion for Swift 5 starts.

David.

> On Fri, May 12, 2017 at 15:51 David Hart via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> Hi swift-evolution,
> 
> Adrian Zubarev and I have discussed several issues with string literals still unresolved after the multi-line string literals proposals and we believe that they are important enough to address for Swift 4. Here is the pitch for our proposal.
> 
> Please let us know what you think:
> 
> https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md>
> 
> Improve String Literals
> 
> Proposal: SE-XXXX <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md>
> Authors: David Hart <https://github.com/hartbit>, Adrian Zubarev <https://github.com/devandartist>
> Review Manager: TBD
> Status: TBD
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#introduction>Introduction
> 
> This proposal builds on top the new features of SE-0168 Multi-Line String Literals <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/0168-multi-line-string-literals.md> by widening the use-cases for unescaped double-quotes and resolving certain issues around long lines in single and multi-line string literals.
> 
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#motivation>Motivation
> 
> In Swift 3, String literals have three pain points:
> 
> Strings containing double-quotes
> Multi-line strings
> Long single-line strings
> Proposal SE-0168 <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/0168-multi-line-string-literals.md> fixed the two first problems with the same syntax. Unfortunately, while an improvement on Swift 3, several problems remain:
> 
> Long single-line strings still require the less than ideal concatenation syntax:
> Some project styles (like the Standard Library) mandate a maximum line length, requiring long single-line strings to be hard-wrapped. This still requires odd solutions:
> 
> assert(condition, "This is a long assertion message that requires " +
>     "string concatenation when the project style enforces maximum line " +
>     "lengths")
> Long lines in a multi-line strings can't be manually wrapped:
> let markdown = """
>     # Title
> 
>     Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer elementum commodo sem, a congue orci porta sit amet. Duis facilisis, est et vehicula congue, turpis dui ultricies nunc, ut elementum quam elit nec felis. Integer aliquam id risus nec laoreet. Vivamus vitae odio sit amet quam iaculis fermentum nec sed neque.
> 
>     ## Subtitle
> 
>     Cras et nibh velit. Praesent eleifend sagittis quam, pellentesque lobortis lectus commodo vel. Vivamus suscipit, nulla quis blandit ullamcorper, velit neque euismod nibh, nec blandit mi diam molestie ex. Cras porttitor, est sed pharetra interdum, ipsum mauris viverra quam, sit amet eleifend purus elit sit amet odio.
>     """
> Short strings containing double-quotes have to use the multi-line syntax to benefit from unescaped double-quotes:
> print("""
>     { "success": false, "error": "Wrong parameter" }
>     """)
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#proposed-solution>Proposed solution
> 
> By implementing multi-line string literals and support for unescaped double-quotes with the same syntax, SE-0168 <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/0168-multi-line-string-literals.md> has made those features unusable on their own. By dissociating them and supporting two extra syntax features, we can solve all the above problems:
> 
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#divorce-the--delimiter-from-the-multi-line-syntax-and-have-them-only-support-unescaped-double-quotes>Divorce the """ delimiter from the multi-line syntax and have them only support unescaped double-quotes
> 
> The change allows us to express short strings containing double-quotes without resorting to the multi-line syntax:
> 
> print("""{ "success": false, "error": "Wrong parameter" }""")
> As a consequence, multi-line strings are now only defined by a newline following the leading delimiter and the whitespace preceeding the trailing delimiter. They gain support for " delimiters, which has the nice advantage of saving a few characters in multi-line strings which are known to never contain double-quotes:
> 
> print("""
>     Triple " are still valid delimiters
>     """)
> 
> query("
>     SELECT 'name'
>     FROM 'people'
>     WHERE age > 20
>     ")
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#support-escaping-newlines-in-multi-line-strings-with-a-trailing->Support escaping newlines in multi-line strings with a trailing \
> 
> This change allows hard-wrapping long lines in multi-line strings. They also have the added benefit of making trailing white-space at the end of source-code lines explicit.
> 
> let markdown = """
>     # Title
> 
>     Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer \
>     elementum commodo sem, a congue orci porta sit amet. Duis facilisis, est \
>     et vehicula congue, turpis dui ultricies nunc, ut elementum quam elit nec \
>     felis. Integer aliquam id risus nec laoreet. Vivamus vitae odio sit amet \
>     quam iaculis fermentum nec sed neque.
> 
>     ## Subtitle
> 
>     Cras et nibh velit. Praesent eleifend sagittis quam, pellentesque \
>     lobortis lectus commodo vel. Vivamus suscipit, nulla quis blandit \
>     ullamcorper, velit neque euismod nibh, nec blandit mi diam molestie \
>     ex. Cras porttitor, est sed pharetra interdum, ipsum mauris viverra \
>     quam, sit amet eleifend purus elit sit amet odio.
>     """
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#adopt-the-cobjective-c-syntax-that-concatenates-single-line-strings>Adopt the C/Objective-C syntax that concatenates single-line strings
> 
> This change will be familiar to C developers and provides a cleaner and more performant solution for long single-line strings:
> 
> assert(condition, "This is a long assertion message that flows "
>     "from one line to the next without requiring the concatenation "
>     "operator")
> 
> assert(condition, """This is another "single-line" message that """
>     """supports up to two double-quotes (" and "") without any """
>     """escaping""")
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#source-compatibility>Source compatibility
> 
> This feature is purely additive; it has no effect on source compatibility.
> 
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#effect-on-abi-stability>Effect on ABI stability
> 
> This feature is purely additive; it has no effect on ABI stability.
> 
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#effect-on-api-resilience>Effect on API resilience
> 
> This feature is purely additive; it has no effect on API resilience.
> 
>  <https://github.com/hartbit/swift-evolution/blob/literal-string-improvements/proposals/XXXX-improve-string-literals.md#alternatives-considered>Alternatives considered
> 
> A different syntax for supporting long single-line strings was discussed where ending delimiters were replaced with the \escaping character, mirroring their use in multi-line strings:
> 
> assert(condition, "This is a long assertion message that flows \
>     "from one line to the next without requiring the concatenation \
>     "operator")
> 
> assert(condition, """This is another "single-line" message that \
>     """supports up to two double-quotes (" and "") without any \
>     """escaping""")
> That syntax saved two characters per line in strings with """ delimiters but had several disadvantages:
> 
> It loses the familiarity with C syntax
> It introduces an asymmetry between the last line and those above
> It does not do any actual escaping, introducing developer ambiguity with their use in multi-line literals
> 
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