Structure instance property value

Question

I can update property value of class instance using dot notation However It doesn't work for structure.

Here is example:

struct Resolution {
    var width = 0

}

class VideoMode {
  var interlaced = false
 }


let someResolution = Resolution()
let someVideoMode = VideoMode()

For class:

someVideoMode.interlaced // false
someVideoMode.interlaced = true //true
someVideoMode.interlaced // now true

For Struct :

 someResolution.width // 0
 someResolution.width  = 200 // throws an error says : someResolution is constant

Question is :

someResolution and someVideoMode both are constants. I can change the property value of class instance without error not saying someVideoMode is constant.However I can not change the property value of struct.It throws an error says someResolution is constant

Why ?

Thank you !

check `valueOfStructInstance` definition is not `let` because this code compiles without any error — Özgür Ersil, Dec 04 '16 at 15:46

shallowThought · Accepted Answer · 2016-12-04T16:35:23.913

0

structs are Value types, while classes are References.

While you can set properties of a constant reference type, you can not change the reference itself.

let someVideoMode = VideoMode()
someVideoMode = VideoMode()

would cause an error.

You can find a detailed description in the documentation you actually got this sample from.

edited Dec 04 '16 at 16:35

answered Dec 04 '16 at 15:54

shallowThought

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Changing let to var fix the problem but in class instance why does it not throw an error ? it is let there too. – Dec 04 '16 at 15:56
Updated answer. – shallowThought Dec 04 '16 at 16:01
Thank you so much ! – Dec 04 '16 at 16:34

Structure instance property value

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