[swift-evolution] [Discussion] Replacing Equal Signs with Colons For Attribute Arguments

[Charles Kissinger]

> On Feb 16, 2016, at 4:08 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Ricardo,
> 
> This proposal is so narrow that I believe *every single example possible* is already in there under motivation. Just sub out each "=" for ":" and you have the entire extent of the change.

Hi Erica,

I think Ricardo means full examples of the new style, including @ symbol, attribute-name, parens, attribute argument label and example attribute arguments. There are no full examples in the proposal of either the existing or proposed style.

It might seem nit-picky (and it is :-)), but that’s the only way for us to evaluate how it will actually look in practice. (Yes, we could look up a few and type them in somewhere ourselves, but it would be nice to have them in the proposal.)

—CK
 
> 
> -- Erica
> 
>> On Feb 16, 2016, at 5:03 PM, Ricardo Parada <rparada at mac.com <mailto:rparada at mac.com>> wrote:
>> 
>> Hi Erica,
>> 
>> I understand this is a draft and even though it may be obvious to many, I would add a few examples with the proposed solution.
>> 
>> Thanks
>> Ricardo Parada
>> 
>> 
>>> On Feb 16, 2016, at 5:42 PM, Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> Thoughts and feedback appreciated. Thank you, -- Erica
>>> 
>>> 
>>> 
>>> Replacing Equal Signs with Colons For Attribute Arguments
>>> 
>>> Proposal: TBD
>>> Author(s): Erica Sadun <http://github.com/erica>
>>> Status: TBD
>>> Review manager: TBD
>>>  <https://gist.github.com/erica/d96011a5c22d9b995b91#introduction>Introduction
>>> 
>>> Attribute arguments are unlike other Swift language arguments. At the call site, they use = instead of colons to distinguish argument names from passed values. This proposal brings attributes into compliance with Swift standard practices by replacing the use of "=" with ":" in this one-off case.
>>> 
>>> Discussion took place on the Swift Evolution mailing list in the [Discussion] Replacing Equal Signs with Colons For Attribute Arguments thread. Thanks to Doug Gregor <https://github.com/DougGregor> for suggesting this enhancement.
>>> 
>>>  <https://gist.github.com/erica/d96011a5c22d9b995b91#motivation>Motivation
>>> 
>>> Attributes enable developers to annotate declarations and types with keywords that constrain behavior. Recognizable by their at-sign <http://foldoc.org/strudel> "@" prefix, attributes communicate features, characteristics, restrictions, and expectations of types and declarations to the Swift compiler. Common attributes include @noescape for parameters that cannot outlive the lifetime of a call, @convention, to indicates whether a type's calling conventions follows a Swift, C, or (Objective-C) block model, and @available to enumerate a declaration's compatibility with platform and OS versions. Swift currently offers about a dozen distinct attributes, and is likely to expand this vocabulary in future language updates.
>>> 
>>> Some attributes accept arguments: @attribute-name(attribute-arguments) including @available and @warn_unused_result. In the current grammar, an equal sign separates attribute argument keywords from values:
>>> 
>>> introduced=version-number
>>> deprecated=version-number
>>> obsoleted=version-number
>>> message=message
>>> renamed=new-name
>>> mutable_variant=method-name
>>> Using = is out of step with other Swift parameterization call-site patterns. Tweaking the grammar to match the rest of Swift introduces a small change that adds consistency across the language.
>>> 
>>> parameter name: parameter value
>>>  <https://gist.github.com/erica/d96011a5c22d9b995b91#detail-design>Detail Design
>>> 
>>> This proposal replaces the use of = with : in the balanced tokens used to compose an attribute argument clause along the following lines:
>>> 
>>> attribute → @ attribute-name attribute-argument-clause<sub>opt</sub>
>>> attribute-name → identifier
>>> attribute-argument-clause → ( balanced-tokens<sub>opt<opt> )
>>> balanced-tokens → balanced-token
>>> balanced-tokens → balanced-token, balanced-tokens
>>> balanced-token → attribute-argument-label : attribute argument-value
>>> This design can be summarized as "wherever current Swift attributes use =, use : instead".
>>> 
>>>  <https://gist.github.com/erica/d96011a5c22d9b995b91#alternatives-considered>Alternatives Considered
>>> 
>>> There are no alternatives to put forth other than not accepting this proposal.
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>>> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
>>> https://lists.swift.org/mailman/listinfo/swift-evolution <https://lists.swift.org/mailman/listinfo/swift-evolution>
>> 
> 
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