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

[Howard Lovatt]

+1 nice additional consistency

On Wednesday, 17 February 2016, Erica Sadun via swift-evolution <
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.
>


-- 
-- Howard.
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