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auto merge of #8884 : blake2-ppc/rust/exact-size-hint, r=huonw

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The message of the first commit explains (edited for changed trait name):

The trait `ExactSize` 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

`ExactSize` 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).

---

It may seem complicated just to solve these small "niggles",
(It's really the reversible enumerate case that's the most interesting)
but only a few core iterators need to implement this trait.

While we gain more capabilities generically for some iterators,
it becomes a tad more complicated to figure out if a type has
the right trait impls for it.
This commit is contained in:
bors 2013-09-03 06:56:05 -07:00
commit 1ac8e8885b
10 changed files with 160 additions and 63 deletions
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47
src/libstd/vec.rs
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@ -274,7 +274,7 @@ impl<'self, T> Iterator<&'self [T]> for RSplitIterator<'self, T> {
return Some(self.v);
}
match self.v.rposition(|x| (self.pred)(x)) {
match self.v.iter().rposition(|x| (self.pred)(x)) {
None => {
self.finished = true;
Some(self.v)
@ -832,7 +832,6 @@ pub trait ImmutableVector<'self, T> {
fn initn(&self, n: uint) -> &'self [T];
fn last(&self) -> &'self T;
fn last_opt(&self) -> Option<&'self T>;
fn rposition(&self, f: &fn(t: &T) -> bool) -> Option<uint>;
fn flat_map<U>(&self, f: &fn(t: &T) -> ~[U]) -> ~[U];
unsafe fn unsafe_ref(&self, index: uint) -> *T;
@ -1048,21 +1047,6 @@ impl<'self,T> ImmutableVector<'self, T> for &'self [T] {
if self.len() == 0 { None } else { Some(&self[self.len() - 1]) }
}
/**
* Find the last index matching some predicate
*
* Apply function `f` to each element of `v` in reverse order. When
* function `f` returns true then an option containing the index is
* returned. If `f` matches no elements then None is returned.
*/
#[inline]
fn rposition(&self, f: &fn(t: &T) -> bool) -> Option<uint> {
for (i, t) in self.rev_iter().enumerate() {
if f(t) { return Some(self.len() - i - 1); }
}
None
}
/**
* Apply a function to each element of a vector and return a concatenation
* of each result vector
@ -1145,7 +1129,7 @@ impl<'self,T:Eq> ImmutableEqVector<T> for &'self [T] {
/// Find the last index containing a matching value
#[inline]
fn rposition_elem(&self, t: &T) -> Option<uint> {
self.rposition(|x| *x == *t)
self.iter().rposition(|x| *x == *t)
}
/// Return true if a vector contains an element with the given value
@ -2319,6 +2303,9 @@ iterator!{impl VecIterator -> &'self T}
double_ended_iterator!{impl VecIterator -> &'self T}
pub type RevIterator<'self, T> = Invert<VecIterator<'self, T>>;
impl<'self, T> ExactSize<&'self T> for VecIterator<'self, T> {}
impl<'self, T> ExactSize<&'self mut T> for VecMutIterator<'self, T> {}
impl<'self, T> Clone for VecIterator<'self, T> {
fn clone(&self) -> VecIterator<'self, T> { *self }
}
@ -2923,16 +2910,6 @@ mod tests {
assert!(v1.position_elem(&4).is_none());
}
#[test]
fn test_rposition() {
fn f(xy: &(int, char)) -> bool { let (_x, y) = *xy; y == 'b' }
fn g(xy: &(int, char)) -> bool { let (_x, y) = *xy; y == 'd' }
let v = ~[(0, 'a'), (1, 'b'), (2, 'c'), (3, 'b')];
assert_eq!(v.rposition(f), Some(3u));
assert!(v.rposition(g).is_none());
}
#[test]
fn test_bsearch_elem() {
assert_eq!([1,2,3,4,5].bsearch_elem(&5), Some(4));
@ -3212,20 +3189,6 @@ mod tests {
};
}
#[test]
#[should_fail]
fn test_rposition_fail() {
let v = [(~0, @0), (~0, @0), (~0, @0), (~0, @0)];
let mut i = 0;
do v.rposition |_elt| {
if i == 2 {
fail!()
}
i += 1;
false
};
}
#[test]
#[should_fail]
fn test_permute_fail() {