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Replace more Iterator for-loops with fold. #3

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Replace more Iterator for-loops with fold. #3

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37 changes: 17 additions & 20 deletions src/libcore/iter/iterator.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -190,9 +190,7 @@ pub trait Iterator {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn last(self) -> Option<Self::Item> where Self: Sized {
let mut last = None;
for x in self { last = Some(x); }
last
self.fold(None, |_, x| Some(x))
}

/// Consumes the `n` first elements of the iterator, then returns the
Expand Down Expand Up @@ -1228,13 +1226,14 @@ pub trait Iterator {
let mut left: B = Default::default();
let mut right: B = Default::default();

for x in self {
// Use fold to enable iterator-specific implementations.
self.fold((), |_, x| {
if f(&x) {
left.extend(Some(x))
left.extend(Some(x));
} else {
right.extend(Some(x))
right.extend(Some(x));
}
}
});

(left, right)
}
Expand Down Expand Up @@ -1794,10 +1793,10 @@ pub trait Iterator {
let mut ts: FromA = Default::default();
let mut us: FromB = Default::default();

for (t, u) in self {
self.fold((), |_, (t, u)| {
ts.extend(Some(t));
us.extend(Some(u));
}
});

(ts, us)
}
Expand Down Expand Up @@ -2116,7 +2115,7 @@ pub trait Iterator {
/// commonalities of {max,min}{,_by}. In particular, this avoids
/// having to implement optimizations several times.
#[inline]
fn select_fold1<I,B, FProj, FCmp>(mut it: I,
fn select_fold1<I,B, FProj, FCmp>(it: I,
mut f_proj: FProj,
mut f_cmp: FCmp) -> Option<(B, I::Item)>
where I: Iterator,
Expand All @@ -2126,17 +2125,15 @@ fn select_fold1<I,B, FProj, FCmp>(mut it: I,
// start with the first element as our selection. This avoids
// having to use `Option`s inside the loop, translating to a
// sizeable performance gain (6x in one case).
it.next().map(|mut sel| {
let mut sel_p = f_proj(&sel);

for x in it {
let x_p = f_proj(&x);
if f_cmp(&sel_p, &sel, &x_p, &x) {
sel = x;
sel_p = x_p;
let mut projected = it.map(|x| (f_proj(&x), x));
projected.next().map(|(sel_p, sel)| {
projected.fold((sel_p, sel), |(sel_p, sel), (x_p, x)| {
if f_cmp(&sel_p, &sel, &x_p, &x) {
(x_p, x)
} else {
(sel_p, sel)
}
}
(sel_p, sel)
})
})
}

Expand Down