[Swift language features] Bind mutating functions

[jkurdek]

In Swift, mutating functions are functions that modify the state of a value type (i.e., struct or enum). By default, structures (struct) and enumerations (enum) are value types, meaning they are copied when assigned or passed around.

Because value types are immutable by default, Swift requires explicit marking of functions that modify them with the mutating keyword.

struct Counter {
    var value: Int = 0

    mutating func increment() {
        value += 1
    }
}