Opaque type retain type identity example

opaque_type_retain_type_identity.swift

public protocol Shape {
    associatedtype T
    func draw() -> String
}

class Triangle: Shape {
    typealias T = Int

    func draw() -> String {
        return "Triangle"
    }
}

// Boxed type
func makeTrapezoid1() -> any Shape {
    let triangle = Triangle()
    return triangle
}

// Opaque type retain type identity example
func makeTrapezoid2() -> some Shape {
    let triangle = Triangle()
    return triangle
}

// compile error: use of protocol 'Shape' as a type must be written 'any Shape'
func makeTrapezoid3() -> Shape {
    let triangle = Triangle()
    return triangle
}