> On Jan 5, 2016, at 8:50 PM, Brent Royal-Gordon via swift-evolution
> <[email protected]> wrote:
>
>> Taking inspiration from syntax used for methods in classes that override
>> methods in superclasses, require methods that override dynamically
>> dispatched default implementations in protocol extensions to use the
>> override keyword. Likewise, forbid the override keyword if the method being
>> implemented instead 'masks' (would that be the right word?) a statically
>> dispatched method in a protocol extension which can nonetheless be invoked
>> by upcasting to the protocol.
>
> This has been suggested before, usually in the form of a separate `implement`
> keyword. The main problem is that it makes it impossible to write a protocol
> after the fact which formalizes some existing pattern in the types.
>
> What do I mean by that? Well, imagine you need generic access to the `min`
> and `max` static properties of the various integer types. There's no existing
> protocol that includes those members. But you can write one and then extend
> the integer types to conform to your new protocol:
>
> protocol BoundedIntegerType: IntegerType {
> static var min: Self { get }
> static var max: Self { get }
> }
> extension Int: BoundedType {}
> extension Int8: BoundedType {}
> extension Int16: BoundedType {}
> extension Int32: BoundedType {}
> extension Int64: BoundedType {}
>
> func printLowestPossibleValueOfValue<Integer: BoundedIntegerType>(x:
> Integer) {
> print(Integer.min)
> }
>
> This only works because `min` and `max` *don't* need any special marking to
> be used to satisfy a requirement. Requiring a keyword like you suggest would
> remove that feature.
Possible solution: if you want a new protocol adoption to map to some existing
method or property then you must explicitly write that. You can't just adopt
the protocol in an empty extension.
extension Int: BoundedType {
static var min = Int.min
static var max = Int.max
}
but with some other syntax that isn't ambiguous. Code completion and compiler
fix-its could suggest this when the class already implements something suitable.
--
Greg Parker [email protected] Runtime Wrangler
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