[swift-users] Swift 4 protocol with associatedtype conforming to itself

[Jens Persson via swift-users]

In Swift 4:

protocol P1 {
    associatedtype A: P1 // Error: Type may not reference itself as a
requirement
}
protocol P2 {
    associatedtype A where A: P2 // OK
}

What is the rationale behind this?

/Jens

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