On 4/22/13 5:48 PM, Diggory Hardy wrote:
Please don't use HTML when posting to lists.
Sorry. I hope this one goes in plain text. (Added a text domain to
Thunderbird.)
2) function parameter types or return type that are not type parameters have
all the same implicit lifetime by default, but they can be qualified
explicitly with some lifetime.
That would mean that a function with default-lifetime parameters taking two
borrowing references could not be called when the two parameters have different
lifetime, if I understand correctly (though I am not aware of the whole
situation). Example:
fn f<'l>(x : & 'l int, y : & 'l int) -> & 'l int {
x
}
This case would be written, with the same meaning, as:
fn f(x : &int, y : &int) -> &int {
x
}
fn caller<'l>(x : & 'l int) -> & 'l int {
let y = 2;
f(x, &y)
}
fn caller(x : &int) -> &int {
let y = 2;
f(x, &y)
}
fn main() {
let x = 5;
io::println(fmt!("%i", *caller(&x)));
}
(This fails, but giving parameter y an independent lifetime makes it succeed.)
And would fail for the same reason. We would want to write, in the new
proposal:
fn f(x : &int, y : &'int) -> &int {
x
}
or
fn f(x : &'int, y : &int) -> &'int {
x
}
and
fn caller(x : &int) -> &int {
let y = 2;
f(x, &y)
}
And it would work as desired with quite less noise (with just one or two
' more than the plain version without lifetimes).
Regards,
Paulo
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