[swift-evolution] [Pitch] Remove associated type inference

David Hart david at hartbit.com
Wed May 25 16:52:21 CDT 2016

> On 25 May 2016, at 23:47, Dmitri Gribenko <gribozavr at gmail.com> wrote:
> On Wed, May 25, 2016 at 2:43 PM, David Hart via swift-evolution
> <swift-evolution at swift.org> wrote:
>> 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.
> Please show an example -- for example, what a smallest collection type
> will look like.

Isn’t that the example in the Detailed Design section? What other example were you thinking of?

>> Alternatives Considered
>> The only alternative is to keep the inference with the known consequences on
>> the compiler.
> Sorry, that's not fair :)  There is a middle ground -- limited
> inference.  For example, in Collection, we don't need Index to be
> inferrable from every declaration that mentions it.  We can add a
> feature to declare that the type of 'var startIndex' infers
> 'associatedtype Index' (via an appropriate attribute).  It is true
> that this approach would not remove global inference as such, but it
> will make it a much easier problem I believe.

This sounds like a more complicated solution: it does not remove global inference and complicates the language with an additional attribute only to help the compiler. I don’t see many advantages to this solution.

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