I understand as per a previous discussion that the owned box ~[T] doesn't
quite have the semantics of a unique *pointer*. Below include my successes
in some borrowing scenarios and analogous failed attempts at borrowing a
reference to a unique pointer to an array within a FooVec struct. How do I
do this? Is there a borrow() type function/method provided for owned boxes
somewhere? (I see some borrow() stuff within the libstd source, but doesn't
seem to be relevant.)
--------------------------------------------------
fn main() {
let a : ~[int] = ~[1,2,3];
// WORKS (borrow1 style below)
let b : &[int] = a;
}
fn do_borrow<'a, T>(t : &'a T) -> &'a T {
t
}
struct Foo(~int);
impl Foo {
fn borrow1<'a>(&'a self) -> &'a int {
match (self) {
// error: mismatched types: expected `&'a int` but found `~int`
// (expected &-ptr but found ~-ptr)
&Foo(ref v) => *v
}
}
fn borrow2<'a>(&'a self) -> &'a int {
match (self) {
// WORKS
&Foo(ref v) => &**v
}
}
fn borrow3<'a>(&'a self) -> &'a int {
match (self) {
// WORKS
&Foo(ref v) => do_borrow(*v)
}
}
}
struct FooVec(~[int]);
impl FooVec {
fn borrow1<'a>(&'a self) -> &'a [int] {
match (self) {
// error: mismatched types: expected `&'a [int]` but found
// `~[int]` ([] storage differs: expected &'a but found ~)
&FooVec(ref v) => *v
}
}
fn borrow2<'a>(&'a self) -> &'a [int] {
match (self) {
// error: type ~[int] cannot be dereferenced
&FooVec(ref v) => &**v
}
}
fn borrow3<'a>(&'a self) -> &'a [int] {
match (self) {
// error: mismatched types: expected `&'a [int]` but found
// `&<V2>` (expected vector but found &-ptr)
&FooVec(ref v) => do_borrow(*v)
}
}
}
--------------------------------------------------
_______________________________________________
Rust-dev mailing list
[email protected]
https://mail.mozilla.org/listinfo/rust-dev
