在 Swift 中复制具有值的变量

Question

I have a variable declared in this way

var model: cellModelCollection<AnyObject, collectionViewCell>

I want to create another variable modelCopy with the same values as model but if I delete an item from modelCopy I don't want it to be deleted from model .

let modelCopy = model don't work.

I also tried to create a struct s

a.model = self.model
b.model = self.model
//delete an item from a.model
print (a.model.count) // 32
print (b.model.count) // 32  element also deleted from b

Answer 1

Your cellModelCollection should be of type struct , not class . Structures are always copied when they are passed around in your code, and do not use reference counting. Check example below in storyboard. You will see that print will produce different results.

struct Model {
    var arg = [0, 1, 2]
}
struct Struct {
    var model: Model?
}

var myStruct1 = Struct()
var myStruct2 = Struct()
var myModel = Model()

myStruct1.model = myModel
myModel.arg.removeLast()
myStruct2.model = myModel

print(myStruct1.model!.arg)
print(myStruct2.model!.arg)

This gives result:

[0, 1, 2]
[0, 1]

BUT if you change struct Model to class Model then result of printing will be the same:

[0, 1]
[0, 1]