Swift function parameters as local variables - swift

Question

I am learning some of the fine point of Swift. On function parameters, the documentation says:
Function parameters are constants by default.
… and proceeds to discuss in-out parameters, which I suppose are Swift’s version of reference parameters.
In other languages, parameters behave as local variables, so you can do this with impunity:
func test(a: Int) {
a = a + 1 // cannot assign to a
print(a*2)
}
var x = 3
test(x)
print(x) // -> 3 as before
I know I can easily create local variables, but is there a Swift equivalent to parameters as local variables?
Note:
The SO description for the parameter tag even uses the word “label”:
Parameters are a type of variable used in a subroutine to refer to the data provided as input to the subroutine.

Answer 1

Before Swift 3, Swift used to have them. You used to be able to do something like this:
func f(var x: Int) { // note the "var" modifier here
x += 1
print(x) // prints 2
}
var a = 1
f(a)
print(a) // prints 1
But it was removed in Swift 3, via SE-0003. The Swift community decided that this is not a good feature. The motivations given in that proposal are:
var is often confused with inout in function parameters.
var is often confused to make value types have reference semantics.
Function parameters are not refutable patterns like in if-, while-, guard-, for-in-, and case statements.

Answer 2

Not sure I understood what do you try to achieve, but if you want to modify external x (so it would be not 3 as before), then you have to make function parameter as inout:
func test(_ a: inout Int) {
a = a + 1 // no error anymore
print(a*2)
}
var x = 3
test(&x)
print(x) // -> 4
Update:
func test(_ a: Int) {
var a = a // make read-write
a = a + 1
print(a*2)
}
var x = 3
test(x)
print(x) // -> 3 as before