Tony & Haravikk,
(Reformatting your quoted examples just a bit…)
>> It enables things like:
>> func someMethod<S : SequenceType, T>(value: S) -> AnySequence<T>
>> where S.Generator.Element == T { ... }
>
> I'm not assuming that. Under the current syntax, I would format your example
> as:
>
> func someMethod<
> S : SequenceType, T
> where S.Generator.Element == T
> >(value: S) -> AnySequence<T> {
> ...
> }
You are both right here, but please note that the proposal still also allows
moving all constraints to the `where` clause:
func someMethod<S, T>(value: S) -> AnySequence<T>
where S : SequenceType,
S.Generator.Element == T
{
...
}
just like Swift 2 allows doing so within the `<...>` brackets:
func someMethod<S, T
where S : SequenceType, S.Generator.Element == T
>(value: S) -> AnySequence<T> {
...
}
The reason I'd recommend that style for anything but simple constraints is
because:
1) It makes the call site `let items = someMethod(value: things)` lightest to
visually match to the declaration, because the only thing between the function
name and its argument list is the `<...>` bracketed list of introduced generic
types which you'll expect to see in the function signature and constraints.
2) In general, the `where` constraints really apply to the whole function/type
declaration, not just a single generic parameter.
3) It was claimed that all constraints should go right next to the introduction
of the generic parameters. But that isn't the whole case because Swift also
applies implicit constraints onto any generic parameters that are used in
constrained positions. If that wasn't clearly said, take the following example
in Swift 2.x:
func aMethod<S : SequenceType, T where S.Generator.Element == T>(value: S)
-> Set<T> {
return Set(value)
}
That declaration actually makes you wait all the way until the return type
`Set<T>` until you learn that `T` must also necessarily be `Hashable`. So I
don't see how it's that different if the `where` clause isn't right next to the
generic type arguments' introduction:
func aMethod<S, T>(value: S) -> Set<T> // FWIW, this line contains what I
usually have in mind when browsing code.
where // T : Hashable, // (implicit)
S : SequenceType,
S.Generator.Element == T
{
return Set(value)
}
— Pyry
PS. Besides, neither the original example nor mine was really fair; you don't
need `where` for these. Instead, you'd just write:
func someMethod<S : SequenceType>(value: S) ->
AnySequence<S.Generator.Element> {
...
}
which SE-0081 has nothing to argue for or against.
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