Hi there, just wanted to let you know I have a name! It's unfortunate that the
mailing list won't accept the update I've made (this has been the 3rd-ish time
I've tried).
~Robert Widmann
2016/05/02 3:16、David Hart <da...@hartbit.com> のメッセージ:
> 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
> Author(s): David Hart, Developer, Pry Jahkola
> Status: TBD
> Review manager: TBD
> 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
>
> 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.
>
> 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
> {
> ...
> }
> This proposal has no impact on extension declarations with constraints
> because those declarations already have the where clauses right before the
> body. In that regard, the proposal makes the other declarations more
> consistent with extension declarations.
>
> Detailed design
>
> First of all, the grammar of generic-parameter-clause is modified to loose
> the requirement- clause:
>
> generic-parameter-clause → < generic-parameter-list >
>
> The grammar of declarations are then amended to gain the requirement-clause:
>
> function-declaration → function-head function-name
> generic-parameter-clauseopt function-signature requirement-clauseopt
> function-bodyopt
>
> union-style-enum → indirectopt enum enum-name generic-parameter-clauseopt
> type-inheritance-clauseopt requirement-clauseopt {
> union-style-enum-membersopt }
>
> raw-value-style-enum → enum enum-name generic-parameter-clauseopt
> type-inheritance-clause requirement-clauseopt { raw-value-style-enum-members
> *}*
>
> struct-declaration → attributesopt access-level-modifieropt struct
> struct-name generic-parameter-clauseopt type-inheritance-clauseopt
> requirement-clauseopt struct-body
>
> class-declaration → attributesopt access-level-modifieropt finalopt class
> class-name generic-parameter-clauseopt type-inheritance-clauseopt
> requirement-clauseopt class-body
>
> protocol-method-declaration → function-head function-name
> generic-parameter-clauseopt function-signature requirement-clauseopt
>
> protocol-initializer-declaration → initializer-head
> generic-parameter-clauseopt parameter-clause throwsopt requirement-clauseopt
>
> protocol-initializer-declaration → initializer-head
> generic-parameter-clauseopt parameter-clause rethrows requirement-clauseopt
>
> initializer-declaration → initializer-head generic-parameter-clauseopt
> parameter-clause throwsopt requirement-clauseopt initializer-body
>
> initializer-declaration → initializer-head generic-parameter-clauseopt
> parameter-clause rethrows requirement-clauseopt initializer-body
>
> Impact on existing code
>
> This proposal impacts all declarations which contain where clauses expect for
> extension declarations and will therefore require a Fix-It.
>
> Alternatives considered
>
> The first post in the swift-evolution thread originally proposed moving the
> where clause just after the generic type declaration. Since then, the
> original author and many other participants in the thread have agreed that
> the current proposal is superior.
>
> It was also proposed to remove the simple inheritance constraints from the
> generic parameter list, but several arguments were brought up that it would
> complicate declarations of simple generics which only needed inheritance
> constraints.
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