[swift-evolution] Move where clause to end of declaration

[Douglas Gregor]

> On May 2, 2016, at 12:16 AM, David Hart via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Hello swift-evolution,
> 
> I took the pitch originally from Developer to move the where clause out of the generic parameter list, with improvements brought up by Pyry Jahkola, and wrote a proposal for it. I opened a Pull Request, but if anybody wants to bring some modifications to it before it is merged, please let me know what you think:
> 
> Move where clause to end of declaration
> 
> Proposal: SE-XXXX <https://github.com/apple/swift-evolution/blob/master/proposals/XXXX-move-where-expression.md>
> Author(s): David Hart <https://github.com/hartbit>, Developer, Pry Jahkola <https://github.com/hartbit/swift-evolution/blob/move-where-clause/proposals/pyry.jahkola@iki.fi>
> Status: TBD
> Review manager: TBD
>  <https://github.com/hartbit/swift-evolution/blob/move-where-clause/proposals/XXXX-move-where-expression.md#introduction>Introduction
> 
> This proposal suggests moving the where clause to the end of the declaration syntax, but before the body, for readability reasons. It has been discussed at length on the following swift-evolution thread:
> 
> [Pitch] Moving where Clauses Out Of Parameter Lists <https://github.com/hartbit/swift-evolution/blob/move-where-clause/proposals/GMANE_DOWN_FOR_NOW>
>  <https://github.com/hartbit/swift-evolution/blob/move-where-clause/proposals/XXXX-move-where-expression.md#motivation>Motivation
> 
> The where clause in declarations can become quite long. When that happens, it breaks the declaration syntax in two, hurting its readability. There is also no good way of formatting the declaration syntax to make it much better.
> 
>  <https://github.com/hartbit/swift-evolution/blob/move-where-clause/proposals/XXXX-move-where-expression.md#proposed-solution>Proposed solution
> 
> The proposal suggests moving the where clause at the end of the declaration, but before the body of concerned declarations. With the proposed change, where clauses do not impede the main declaration and are also more easily formattable. For example, here is the same function declaration before and after the change: 
> 
> func anyCommonElements<T : SequenceType, U : SequenceType where
>     T.Generator.Element: Equatable,
>     T.Generator.Element == U.Generator.Element>(lhs: T, _ rhs: U) -> Bool where
> {
>     ...
> }
> 
> func anyCommonElements<T : SequenceType, U : SequenceType>(lhs: T, _ rhs: U) -> Bool where
>     T.Generator.Element: Equatable,
>     T.Generator.Element == U.Generator.Element
> {
>     …
Random minor comment: I find that putting the “where” at the end makes this almost unreadable, and would very much have preferred

> func anyCommonElements<T : SequenceType, U : SequenceType>(lhs: T, _ rhs: U) -> Bool
>     where T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element


	- Doug

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