[swift-evolution] Proposals: (1) Forbidding custom `==` for value types, (2) `dispatch` keyword, (3) `default`-result for methods with `Self`, and (4) Poor-Mans-Existentials

[Johannes Neubauer]

> Am 18.07.2016 um 14:01 schrieb Johannes Neubauer via swift-evolution <swift-evolution at swift.org>:
> 
> 
>> Am 18.07.2016 um 13:52 schrieb Johannes Neubauer via swift-evolution <swift-evolution at swift.org>:
>> 
>>> 
>>> Am 18.07.2016 um 13:05 schrieb L. Mihalkovic <laurent.mihalkovic at gmail.com>:
>>> 
>>> IMHO implementing your proposal would close the door on some of the things you do when building in-memory dbs (T == U -> TRUE for T not related to U), which if swift remains for small apps is not a terrible loss, but may be more of an issue for one day doing big-data with it.
>> 
>> You talk about reference types now, right? I proposed a `default` keyword, which (in a pattern matching fashion) would catch all calls to T == U for which no implementation exists (so this is exactly when T != U). You could of course change for a given type hierarchy the `default` result to `true` if appropriate.
> 
> This formulation can be misleading: I mean `a == b` where `a: T` and `b: U` and `T != U`. Due to dynamic dispatch even: `a.dynamicType == T && b.dynamicType == U && T != U`.

But I think, for such a radical different semantic than the normal interpretation of equality I think I wouldn’t use the `Equatable`-protocol at all, but implement a custom protocol with a custom operator.
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