If the pointer is returned all the way up to the main function, then it must be required for the lifetime of the program (or else the program is poorly designed). What point are you trying to make?
Unless you put that pointer in a structure which lives forever, it will be freed as soon as a loop finishes:
struct Foo { a: int, b: int }
impl Drop for Foo {
fn drop(&mut self) {
println!("Drop {:?}", *self);
}
}
fn foo(i: int) -> Foo {
println!("Creating Foo with {}", i);
Foo { a: i, b: 5}
}
fn do_thing(foo: &Foo) {
println!("\tdo thing {:?}", *foo);
}
fn do_other_thing(foo: &Foo) {
println!("\tdo other thing {:?}", *foo);
}
fn main() {
for i in range(0, 5) {
let a = box foo(i);
do_thing(a);
do_other_thing(a);
}
}
Creating Foo with 0
do thing Foo{a: 0, b: 5}
do other thing Foo{a: 0, b: 5}
Drop Foo{a: 0, b: 5}
Creating Foo with 1
do thing Foo{a: 1, b: 5}
do other thing Foo{a: 1, b: 5}
Drop Foo{a: 1, b: 5}
Creating Foo with 2
do thing Foo{a: 2, b: 5}
do other thing Foo{a: 2, b: 5}
Drop Foo{a: 2, b: 5}
Creating Foo with 3
do thing Foo{a: 3, b: 5}
do other thing Foo{a: 3, b: 5}
Drop Foo{a: 3, b: 5}
Creating Foo with 4
do thing Foo{a: 4, b: 5}
do other thing Foo{a: 4, b: 5}
Drop Foo{a: 4, b: 5}
let mut blah = ~MyStruct{x: 3, y: 4};
for i in range(0,100000000) {
blah = ~MyStruct{x: i + blah.x, y: i + blah.y};
}
println!("{} {}", blah.x, blah.y);