> On Dec 23, 2015, at 10:37 AM, Lino Rosa <[email protected]> wrote:
>
> Paul Cantrell: Sure, example below. Changing `struct Position` into `class
> Position` would still compile and print 30 instead.
>
> ==============================
> struct Position {
> var x: Int
> var y: Int
>
> init(x: Int, y: Int) {
> self.x = x
> self.y = y
> }
> }
>
> func move(var position: Position) {
> position.x += 20
> }
>
> var p1 = Position(x: 10, y: 10)
> move(p1)
>
> print(p1.x) // prints 10
> ==============================
Ah, OK, sure … but why is this a problem? You changed the declaration! Of
course it behaves differently. Changing a declaration can transparently change
behavior in any number of circumstances. The following code still compiles if
you change “Int” to “UInt8,” but it crashes:
struct Position {
var x: Int
var y: Int
init(x: Int, y: Int) {
self.x = x
self.y = y
}
}
func move(var position: Position) {
position.x += 200
}
var p1 = Position(x: 100, y: 100)
move(p1)
print(p1.x)
I could see this argument having some traction for protocol extensions, which
can be attached to structs or classes with wildly different results. Protocols
can limit themselves to classes only; can they limit themselves to structs as
well? I don’t think so…. That could be a useful language change.
Cheers, P
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