Swift make method parameter mutable?

Question

How can I deal with this error without creating additional variable?

func reduceToZero(x:Int) -> Int {
    while (x != 0) {
        x = x-1            // ERROR: cannot assign to 'let' value 'x'
    }
    return x
}

I don't want to create additional variable just to store the value of x. Is it even possible to do what I want?

Answer 1

As stated in other answers, as of Swift 3 placing var before a variable has been deprecated. Though not stated in other answers is the ability to declare an inout parameter. Think: passing in a pointer.

func reduceToZero(_ x: inout Int) {
    while (x != 0) {
        x = x-1     
    }
}

var a = 3
reduceToZero(&a)
print(a) // will print '0'

This can be particularly useful in recursion.

Apple's inout declaration guidelines can be found here.