Subscript of a struct doesn't set values when created as an implicitly unwrapped optional

问题:

Why can't I change the the "numbers" array using subscripts when "Foo" is an implicitly unwrapped optional?

struct Foo {     var numbers = [0,0,0]     subscript(index: Int) -> Int {         get { return self.numbers[index] }         set { self.numbers[index] = newValue }     } }   var fooA:Foo! fooA = Foo()  fooA[1] = 1              // does not change numbers array fooA[1]                  // returns 0  fooA.numbers[1] = 1      // this works fooA[1]                  // returns 1  var fooB:Foo! fooB = Foo()  fooB![1] = 1              // this works fooB![1]                  // returns 1 

For some reason it works when I make "Foo" a class (called "Goo" below)

class Goo {     var numbers = [0,0,0]     subscript(index: Int) -> Int {         get { return self.numbers[index] }         set { self.numbers[index] = newValue }     } }  var goo:Goo! goo = Goo()  goo[1] = 1              // this works goo[1]                  // returns 1 

回答1:

it looks like a bug (or i miss something important), check this

struct Foo {     var numbers = [0,0,0]     subscript(index: Int) -> Int {         get {             return self.numbers[index]         }         set {             numbers[index] = newValue         }     } }   var fooA:Foo! = Foo() // here is the difference fooA?[1] = 1 fooA[1]                  //  1 fooA.numbers[1] = 1 fooA[1]                  //  1 

more 'complex' experiment

struct Foo {     var numbers = [0,0,0]     subscript(index: Int) -> Int {         get {             return numbers[index]         }         set {             print(numbers[index],newValue)             numbers[index] = newValue             print(numbers[index])         }     } }   var fooA:Foo! = Foo()  fooA[1] = 1 fooA[1]                  // 0 // but prints // 0 1 // 1 

for more 'fun'

var fooA:Foo! = Foo() if var foo = fooA {     foo[1] = 1     print(foo) } 

prints

"Foo(numbers: [0, 1, 0])\n" 

文章来源: Subscript of a struct doesn't set values when created as an implicitly unwrapped optional