We could have the generic type parameter always shadow the associated type.
> On 26 May 2016, at 06:08, Patrick Smith <pgwsm...@gmail.com> wrote:
>
> While this has been a handy feature, I don’t mind making things more
> explicit, as I think it helps communication. Sometimes clarity that helps the
> compiler will also help the reader. It’s only really convenient when writing.
>
> I would be happy with this change as long as the issue with same named
> generics were changed. Currently in Swift 2.2 I can’t do this:
>
> struct SomeGenericGenerator<Element> : GeneratorType {
> typealias Element = Element // Error: Type alias ‘Element’ circularly
> references itself
> }
>
> It’s a real pain, as now I have to think up some alternate name for the
> generic parameter ‘Element’.
>
> Whereas, with automatic inference, I can do this without the compiler
> complaining:
>
> struct SomeGenericGenerator<Element> : GeneratorType {
> mutating func next() -> Element? {
> return nil
> }
> }
>
> So I’d like to see the above `typealias Element = Element` allowed if
> possible.
>
>
>> On 26 May 2016, at 7:43 AM, David Hart via swift-evolution
>> <swift-evolution@swift.org> wrote:
>>
>> Here’s a pitch for removing associated type inference as per the Generics
>> Manifesto. If we want to do it, we’d better do it before Swift 3:
>>
>> Remove associated type inference
>> Proposal: SE-XXXX
>> Author: David Hart, Douglas Gregor
>> Status: TBD
>> Review manager: TBD
>> Introduction
>>
>> This proposal seeks to remove the inference of associated types in types
>> conforming to protocols.
>>
>> Motivation
>>
>> Even if associated types inference in a useful feature, it is also a big
>> source of bugs in the compiler. This proposal argues that the usefulness
>> does not outweight its architectural complexity. As per the Generics
>> Manifesto:
>>
>> associated type inference is the only place in Swift where we have a global
>> type inference problem: it has historically been a major source of bugs, and
>> implementing it fully and correctly requires a drastically different
>> architecture to the type checker.
>> Because this is a breaking change, it would be beneficial to implement it
>> for Swift 3.
>>
>> Detailed Design
>>
>> The proposal would remove associated type inference and make code which
>> relied on it invalid:
>>
>> protocol IteratorProtocol {
>> associatedtype Element
>> mutating func next() -> Element?
>> }
>>
>> struct IntIterator : IteratorProtocol {
>> mutating func next() -> Int? { ... } // used to infer Element = Int
>> }
>> The compiler would generate an error message stating: error: IntIterator is
>> missing its Element associated type declaration. The code would have to be
>> modified as follows to fix the error:
>>
>> struct IntIterator : IteratorProtocol {
>> typealias Element = Int
>> mutating func next() -> Int? { return nil } // used to infer Element =
>> Int
>> }
>> Impact on Existing Code
>>
>> This is a breaking change that will require conforming types which relied on
>> the inference, including in the Standard Library, to explicitly declare
>> associated types. A Fix-It could be introduced to add the typealias and
>> leave the type to be filled in. That way, all the type inference could be
>> removed from the compiler.
>>
>> Alternatives Considered
>>
>> The only alternative is to keep the inference with the known consequences on
>> the compiler.
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution@swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>
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