Swift のパラメータで参照カウントがどうなっているのかチェックするコード

terminal.sh-session

➜  12:20:40  TOOLCHAINS=com.apple.dt.toolchain.Swift_2_3 swift -Onone ./TestReference2.3.swift
./TestReference2.3.swift:19:10: warning: 'var' parameters are deprecated and will be removed in Swift 3
func buz(var s: S) -> Bool {
         ^~~
         
true
false
true
true
true
false
➜  12:20:44  TOOLCHAINS=com.apple.dt.toolchain.Swift_2_3 swift -O ./TestReference2.3.swift
./TestReference2.3.swift:19:10: warning: 'var' parameters are deprecated and will be removed in Swift 3
func buz(var s: S) -> Bool {
         ^~~
         
true
true
true
true
true
true
➜  12:20:49  swift -Onone ./TestReference3.swift
true
false
true
true
➜  12:20:54  swift -O ./TestReference3.swift
true
true
true
true

TestReference2.3.swift

class C {}

struct S {
    var c = C()
    mutating func checkReference() -> Bool {
        return isUniquelyReferencedNonObjC(&c)
    }
}

func foo(s: S) -> Bool {
    var s = s
    return s.checkReference()
}

func bar(inout s: S) -> Bool {
    return s.checkReference()
}

func buz(var s: S) -> Bool {
    return s.checkReference()
}

var s = S()
//                           -Onone -O
print(s.checkReference()) // true   true
print(foo(s))             // false  true
print(s.checkReference()) // true   true
print(bar(&s))            // true   true
print(s.checkReference()) // true   true
print(buz(s))             // false  true

TestReference3.swift

class C {}

struct S {
    var c = C()
    mutating func checkReference() -> Bool {
        return isKnownUniquelyReferenced(&c)
    }
}

func foo(_ s: S) -> Bool {
    var s = s
    return s.checkReference()
}

func bar(_ s: inout S) -> Bool {
    return s.checkReference()
}

// func buz(_ var s: S) -> Bool {
//     return s.checkReference()
// }

var s = S()
//                           -Onone -O
print(s.checkReference()) // true   true
print(foo(s))             // false  true
print(s.checkReference()) // true   true
print(bar(&s))            // true   true
// print(s.checkReference()) // true   true
// print(buz(s))             // false  true