[swift-evolution] [Discussion] Additional generics specialization

[L. Mihalkovic]

It was TypeScript

Regards
(From mobile)

> On Jul 18, 2016, at 9:48 PM, L. Mihalkovic <laurent.mihalkovic at gmail.com> wrote:
> 
> 
> 
> Regards
> (From mobile)
> 
>> On Jul 18, 2016, at 9:04 AM, Adrian Zubarev via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> This is something additional, but I’m curios about how the community feels about it.
>> 
>> I recently come across the issue where conforming to Hashable wasn’t enough to thecke if two instances of the same generic type were equal.
>> 
>> I had additionally provide myself the != function.
>> 
>> public func !=<T, U>(lhs: SomeTypeName<T>, rhs: SomeTypeName<U>) -> Bool {
>>     return lhs.hashValue != rhs.hashValue
>> }
>> I wondered if Swift can ever get generic specialization like this:
>> 
>> public func !=<T : Hashable, U, V>(lhs: T<U>, rhs: T<V>) -> Bool {
>>     return !(lhs.hashValue == rhs.hashValue)
>> }
> I am not sure about the ordering... Interestingly enough, this is real code written last week as part of a framework:
> 
> Export function newSataStore<T extends DataStore<U>, U> (ctor: { new (config:DataStoreConfig):T, config:DataStoreConfig):T {
>    return new ctor(config)
> }
> 
> And this is legal code just to try:
> 
>  interface Hashable {
>   getHash(): number
> }
> interface T extends Hashable { }
> class SomeTypeName<Type extends Hashable> {
>   public getHash():number {
>     return ...;
>   }
>   public type():this {
>     return Type;
>   }
> }
> function compare<T1 extends T, T2 extends T>(lhs:SomeTypeName<T1>, rhs:SomeTypeName<T2>):boolean {
>   return lhs.getHash() != rhs.getHash();
> }
>  
> but this is more interesting:
> 
> type List<T> = T & { next: List<T> }   // listObj.next.next.next.???
> 
> 
> 
> 
>> This function in stdlib would fill the gap. Or we need an extra protocol GenericHashable which includes !=.
>> 
>> 
>> 
>> -- 
>> Adrian Zubarev
>> Sent with Airmail
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>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
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