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std::iterator: Introduce trait ExactSizeHint

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The trait `ExactSizeHint` is introduced to solve a few small niggles:

* We can't reverse (`.invert()`) an enumeration iterator
* for a vector, we have `v.iter().position(f)` but `v.rposition(f)`.
* We can't reverse `Zip` even if both iterators are from vectors

`ExactSizeHint` is an empty trait that is intended to indicate that an
iterator, for example `VecIterator`, knows its exact finite size and
reports it correctly using `.size_hint()`. Only adaptors that preserve
this at all times, can expose this trait further. (Where here we say
finite for fitting in uint).
This commit is contained in:
blake2-ppc 2013-08-30 19:59:49 +02:00
parent 0ac3e023d8
commit 4b2cc22031
2 changed files with 38 additions and 0 deletions
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3
src/libstd/vec.rs
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@ -2319,6 +2319,9 @@ iterator!{impl VecIterator -> &'self T}
double_ended_iterator!{impl VecIterator -> &'self T}
pub type RevIterator<'self, T> = Invert<VecIterator<'self, T>>;
impl<'self, T> ExactSizeHint for VecIterator<'self, T> {}
impl<'self, T> ExactSizeHint for VecMutIterator<'self, T> {}
impl<'self, T> Clone for VecIterator<'self, T> {
fn clone(&self) -> VecIterator<'self, T> { *self }
}