Constrained associated type on protocol

[xwu (Xiaodi Wu)]

Making a protocol's associated type concrete via inheritance

Apologies for any terminology that I'm not using correctly, but I'm wondering if there's any way to make this work in Swift 4: protocol P1 { associatedtype Thing func makeThing() -> Thing } protocol P2: P1 where Thing == String {} func test(_ p2: P2) { // Can only use P2 as a generic constraint even though P2.Thing should be known to be String print(p2.makeThing()) } I want P2 to conform to P1 and make its associated type concrete so that it can be used directly. If this isn't po…