Swift：结构数组与类数组

Question

I have a swift array of struct and I am unable edit the first property, whereas I am able edit the first property with an array of class.

In order to edit the first object of the struct array, I have to do [0] then .first

I know structs are valued by type, class are value by reference. But I don't understand the different behavior. Can someone explain?

class PersonObj {
    var name = "Dheearj"

}

struct Person  {
    var name = "Dheearj"
    
    mutating func update(name: String){
        self.name = name
    }
}

var array = [Person(),Person()]
array[0].update(name:"dheeraj")
array[0].name = "yuuu"
array.first?.name = "dddddd" <--- "Error Here"

var array1 = [PersonObj(),PersonObj()]
array1.first!.name = "ttt"

print(array1.first?.name ?? "")
print(array.first?.name ?? "")
print(array.count)

Screenshot of the error message:

Answer 1

Mutating a struct stored within some other property behaves as though you've copied out the value, modified it, and overwrote it back into place.

Take this line for example: (I replaced the optional chaining with force unwrapping, for simplicity)

array.first!.name = "dddddd"

It behaves as though you did:

var tmp = array.first!
tmp.name = "dddddd"
array.first = tmp

It's easy to see what that doesn't work. Array.first , is a get-only property (it doesn't have a setter).

The case for classses works because the value stored in the array is a reference to the object, and the reference isn't changing (only the values within the object it refers to, which the array doesn't know or care about).