The errors you are seeing now are in fact related to borrowing @T
values, as suggested in a previous message. In this case, your problem
is that you need to have values with the same lifetime as the this
pointer, but the default match construct copies value out. This means
that the lifetime of the copied-out values is limited to the current
stack frame. You can address this using `ref` mode. Unfortunately, due
to the bug with lifetime inference cited earlier, you will need to
provide explicit hints to help the type checker out. Hopefully this will
be fixed soon.
In any case, I've made the requisite changes here:
https://github.com/nikomatsakis/rustled/commit/aea45eeeea2b328f5f3c6515de21be2039a9498d
and opened a pull request:
https://github.com/stevej/rustled/pull/1
regards,
Niko
Steve Jenson wrote:
On Thu, Dec 27, 2012 at 3:16 PM, Niko Matsakis <[email protected]
<mailto:[email protected]>> wrote:
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.
No problem with reply timing.
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.
Unfortunately not but a much more interesting set of error messages
about lifetimes is coming out now: http://pastebin.com/SYwCw1ac
And here is a link to the each method again (I pushed this broken
version to github so I can share the exact changes I made)
https://github.com/stevej/rustled/blob/master/red_black_tree.rs#L96
Thanks a bunch for all of your clarifying comments and blog posts.
Steve
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