Do instance references really work in Swift?

Question

I wrote the Objective-C code first

NSMutableString *aStrValue = [NSMutableString stringWithString:@\"Hello\"];
NSMutableDictionary *aMutDict = [NSMutableDict         


        

Answer 1

Reference type

The different behaviours depends on the fact that in the Objective-C code you use NSMutableString that is a class. This means that aMutDict and aStrValue are references to the same object of type NSMutableString. So the changes you apply using aStrValue are visibile by aMutDict.

Value type

On the other hand in Swift you are using the String struct. This is a value type. This means that when you copy the value from one variable to another, the change you do using the first variable are not visible to the second one.

The following example clearly describes the value type behaviour:

var word0 = "Hello"
var word1 = word0

word0 += " world" // this will NOT impact word1

word0 // "Hello world"
word1 // "Hello"

Hope this helps.