I'm sorry for not replying more quickly, I was not checking e-mail over
xmas break. I do not know of any general problems with @ and
borrowing. In any event, this is a misdiagnosis.
The problem is this: the declaration of iter looks like this:
impl<K: Copy Eq Ord, V: Copy> RBMap<K, V>: iter::BaseIter<(&K, &V)>
In the context of a type declaration, an & means `&self`, where `self`
is the lifetime parameter associated with the type/impl/whatever (just
as the impl has two type parameters K and V, it also has an implicit
lifetime parameter `self`). So, this declaration written out more
explicitly would be:
impl<K: Copy Eq Ord, V: Copy> RBMap<K, V>: iter::BaseIter<(&self/K,
&self/V)>
However, your method declaration is:
pure fn each(&self, f: fn(&(&K, &V)) -> bool) { ... }
In the context of a function declaration, & means "a fresh lifetime".
So this winds up being short for a declaration life this:
pure fn each(&self, f: fn(&a/(&a/K, &a/V)) -> bool) { ... }
However, the trait declares that `each` should have this type:
pure fn each(&self, f: fn(&a/(&self/K, &self/V)) -> bool) { ... }
So I think that if you change your declaraiton of `each()` to:
pure fn each(&self, f: fn(&(&self/K, &self/V)) -> bool) { ... }
It will work just fine. I apologize for the cryptic error message.
Working on it.
I think the system of defaults regarding types like `&T` needs to
change. I hope that a more explicit notation would make the problem
more obvious. But that's a subject for another e-mail.
Niko
Lucian Branescu wrote:
I think the problem is the compiler can't guarantee the managed box
will survive, so it won't allow a borrowed pointer.
I think there are problems in general with @ and borrowing.
I've converted the red-black tree I wrote to use iter::BaseIter but am
now fighting with lifetime analysis with the switch to 0.5.
https://github.com/stevej/rustled/blob/master/red_black_tree.rs#L91
And the error I'm getting with 0.5 is:
http://pastebin.com/YK8v7EdA
I've read the docs on lifetimes several times now but it's not quite
enough to get me over this hurdle.
Thanks!
Steve
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