(edited)

koher

let N = 10_000_000 public struct Example<Base> { let base: Base public init(_ base: Base) { self.base = base } } public protocol ExampleCompatible { associatedtype CompatibleType var ex: CompatibleType { get } } extension ExampleCompatible { public var ex: Example<Self> { return Example(self) } } public struct Foo { public var a: Int = 1 public var b: Int = 2 public var c: Int = 3 public var d: Int = 4 public var e: Int = 5 public var f: Int = 6 public var g: Int = 7 public var h: Int = 8 public var i: Int = 9 public var j: Int = 10 public init() {} } extension Foo { public var ex_ab: Int { return a + b } } extension Foo: ExampleCompatible { public var ex: Example<Foo> { return Example(self) } } extension Example where Base == Foo { public var ab: Int { return base.a + base.b } } let foo = Foo() var sum = 0 for _ in 0..<N { sum += foo.ex.ab } print(foo)

Version:

swift-4.1.1-RELEASE

Output:

Foo(a: 1, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10)

Error: