[swift-evolution] [Pitch] Moving where Clauses Out Of Parameter Lists

[Sean Heber]

*grabs paintbrush*

Something that has always bothered me about the generic syntax for functions is how far the function’s name is from its parameters. There are probably reasons why the following might not work, but it could address my desire to keep the name of the thing close to the names of the inputs:

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

I haven't given this tons of thought, but this seemed like a good a thread as any to mention my concern about the distance of the name from the parameters. :)

l8r
Sean



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



> On Apr 6, 2016, at 1:30 PM, Developer via swift-evolution <swift-evolution at swift.org> wrote:
> 
> If you've ever gotten to the point where you have a sufficiently generic interface to a thing and you need to constrain it, possibly in an extension, maybe for a generic free function or operator, you know what a pain the syntax can be for these kinds of operations.  For example, the Swift book implements this example to motivate where clauses
> 
> func anyCommonElements <T: SequenceType, U: SequenceType where T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element> (lhs: T, _ rhs: U) -> Bool
> 
> This is noisy and uncomfortable to my eyes, and almost impossible to align correctly.  Per a short discussion on Twitter with Joe Groff and Erica Sadun, I'd like so see what the community feels about moving the where clause out of the angle brackets.  So that example becomes
> 
> func anyCommonElements <T: SequenceType, U: SequenceType>
> where T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element
> (lhs: T, _ rhs: U) -> Bool
> 
> Or, if you're feeling ambitious, even
> 
> func anyCommonElements <T, U>
> where T : SequenceType, U : SequenceType,
> T.Generator.Element: Equatable, T.Generator.Element == U.Generator.Element
> (lhs: T, _ rhs: U) -> Bool
> 
> Thoughts?
> 
> ~Robert Widmann
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