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I'd like a function to return a reference of an array:
var a = [1, 2]
var b = [3, 4]
func arrayToPick(i:Int) -> [Int] {
return i == 0 ? a : b
}
inout var d = arrayToPick(0)
d[0] = 6
println(a[0]) // 1
println(d[0]) // 6
I'm unable to return &a or &b in arrayToPick because those can't be casted to [Int].
How to return a reference on a or b from a function?
306
Swift inout parameter is a parameter that can be changed inside the function where it's passed into. To accept inout parameters, use the inout keyword in front of an argument. To pass a variable as an inout parameter, use the & operator in front of the parameter.
All parameters passed into a Swift function are constants, so you can't change them. If you want, you can pass in one or more parameters as inout , which means they can be changed inside your function, and those changes reflect in the original value outside the function.
Tuples can be used to return multiple values from Swift functions. A tuple allows you to group together multiple values of different types which can then be returned from a function as a single entity.
You cannot return inout value. Because the compiler cannot guarantee the lifetime of the value.
You have unsafe way, like this:
var a = [1, 2]
var b = [3, 4]
func arrayToPick(i:Int) -> UnsafeMutablePointer<[Int]> {
if i == 0 {
return withUnsafeMutablePointer(&a, { $0 })
}
else {
return withUnsafeMutablePointer(&b, { $0 })
}
}
var d = arrayToPick(0)
d.memory[0] = 6
println(a[0]) // -> 6
In this case, after a is deallocated, d.memory access may cause BAD_ACCESS error.
Or safe way, like this:
var a = [1, 2]
var b = [3, 4]
func withPickedArray(i:Int, f:(inout [Int]) -> Void) {
i == 0 ? f(&a) : f(&b)
}
withPickedArray(0) { (inout picked:[Int]) in
picked[0] = 6
}
println(a[0]) // -> 6
In this case, you can access the picked value only in the closure.
115
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