What is the mutating keyword and when is it required?

The mutating keyword in Swift is used to indicate that a method will modify the instance of the struct or enum that it is called on. In Swift, structures and enumerations are value types, meaning that when you assign or pass them around, you are working with a copy of the value. If you want to change a property of a structure or enumeration within its own method, you need to mark that method with the mutating keyword.

It is required when you want to modify properties of a struct or enum within its own method. Without the mutating keyword, the compiler will raise an error because value types are not allowed to modify themselves by default.

Here is an example:


    struct Counter {
        var count = 0
        
        mutating func increment() {
            count += 1
        }
        
        mutating func reset() {
            count = 0
        }
    }
    
    var myCounter = Counter()
    myCounter.increment()
    print(myCounter.count) // Output: 1
    myCounter.reset()
    print(myCounter.count) // Output: 0

mutating Swift structs enums value types

What is the mutating keyword and when is it required?

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What is the mutating keyword and when is it required?

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