Avner Barr Avner Barr - 1 month ago 6
Swift Question

Swift - How to mutate a struct object when iterating over it

I am still not sure about the rules of struct copy or reference.

I want to mutate a struct object while iterating on it from an array:
For instance in this case I would like to change the background color
but the compiler is yelling at me

struct Options {
var backgroundColor = UIColor.blackColor()
}

var arrayOfMyStruct = [MyStruct]

...

for obj in arrayOfMyStruct {
obj.backgroundColor = UIColor.redColor() // ! get an error
}

Answer

struct are value types, thus in the for loop you are dealing with a copy.

Just as a test you might try this:

struct Options {
    var backgroundColor = UIColor.blackColor()
}

var arrayOfMyStruct = [Options]()

for (index, _) in enumerate(arrayOfMyStruct) {
    arrayOfMyStruct[index].backgroundColor = UIColor.redColor() 
}

Here you just enumerate the index, and access directly the value stored in the array.

Hope this helps.