[swift-evolution] Replace named returns with `out` parameters?

[Anton Zhilin]

Some people on the list wondered, why we have moved from tuples in function
parameters, but multiple returns are still implemented using tuples? The
following code still compiles:

func position() -> (x: Int, y: Int) {
    return (x: 0, y: 0)
}
let (y, x) = position()

(Maybe it’s a bad example, because naturally we’d use Point struct. Let’s
pretend those two parameters don’t make sense as a struct.)

What I want to discuss is if we should introduce out parameters *and* make
them the default for multiple returns for Swift 4. The syntax would look
like:

func position(x: out Int, y: out Int) {
    x = 0
    y = 0
}
var y
position(x: let x, y: y)

out arguments can be any patterns allowed on the left side of assignment,
including wildcard pattern and tuple destructuring pattern.
​
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