Is it possible to expand which protocols can act as types?

[xwu (Xiaodi Wu)]

This was just asked four days ago:

Constrained associated type on protocol

Why associated type requirement persists when a constrain is defined on a protocol? For instance: protocol P1 { var id: String { get } } var p1Array: [P1] // OK protocol P2: Identifiable where Self.ID == String { } var p2Array: [P2] // Protocol 'P2' can only be used as a generic constraint because it has Self or associated type requirements Thank you