Learning Swift™ Programming

Mutating Methods

If a method inside a struct will alter a property of the struct itself, it must be declared as mutating. This means that if the struct has some property that belongs to the struct itself (not a local variable inside a method) and you try to set that property, you will get an error unless you mark that method as mutating. Here’s a struct that will throw an error:

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struct someStruct {    var property1 = "Hi there"    func method1() {        property1 = "Hello there" // property1 belongs to the class itself           so we can't change this with making some changes    }    // ERROR: cannot assign to 'property1' in 'self'}

The fix for this error is simple. Just add the word mutating in front of the