On Wednesday, 5 February 2014 at 00:50:55 UTC, Walter Bright
wrote:
Again, what happens with:
T identity(T t) { return t; }
? I.e. the transference of the argument pointer type to the
return type?
As far as I see, in Rust the pointer type is lost on the return
value as well, if your function takes a reference (borrowed
pointer). But you can do:
fn identity(x: &T) -> T {
return *T;
}
fn main() {
let a = ~T;
let r = ~identity(a);
}
That is: pass by reference and return a value type. If you then
pass an owned pointer ~T, you can directly construct the returned
value in heap allocated memory ~identity(a) and assign the
resulting owned pointer. The compiler is smart enough to not do
unnecessary copies.
That way the caller is responsible for the relationship between
argument pointer type and result pointer type.
With a single function, you can freely mix all combinations of
argument and return types. E.g. pass an owned pointer and
construct a Gc<T> from the returned result.
