func foo<T: P>(_: T) extension P { func _forwardToFoo() { foo(self) } } func callFooOnEach(_ ps: [P]) { for p in ps { p._forwardToFoo() } }

3:36 AM

PのExisはP自身にconformしないが、extensionの中のselfを介してconformさせられる技

3:37 AM

ネタ元 https://forums.swift.org/t/lifting-the-self-or-associated-type-constraint-on-existentials/18025/18?u=omochimetaru

Lifting the "Self or associated type" constraint on existentials

It's awkward, but you can in fact "open" the existential by invoking a protocol extension method, which will give you Self as the dynamic type of the value inside the method, which you can then pass to generic functions: func foo(_: T) extension P { func _forwardToFoo() {...

3:37 AM

↑existensialのassoctype制約を無くすピッチ

3:39 AM

昔々から今までできなかったのは技術的な理由で、PWTがassoctypeを持ってなかったからで、今はそこがクリアされてるらしい