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std::vec: Sane implementations for connect_vec and concat_vec

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Avoid unnecessary copying of subvectors, and calculate the needed space
beforehand. These implementations are simple but better than the
previous.

Also only implement it once, for all `Vector<T>` using:

    impl<'self, T: Clone, V: Vector<T>> VectorVector<T> for &'self [V]

performance improved according to the bench test:

    before
    test vec::bench::concat ... bench: 74818 ns/iter (+/- 408)
    test vec::bench::connect ... bench: 87066 ns/iter (+/- 376)

    after
    test vec::bench::concat ... bench: 17724 ns/iter (+/- 126)
    test vec::bench::connect ... bench: 18353 ns/iter (+/- 691)

Closes #9581
This commit is contained in:
blake2-ppc 2013-09-28 04:15:40 +02:00
parent 5444f601dc
commit 24a4d0daf0
1 changed files with 15 additions and 26 deletions
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41
src/libstd/vec.rs
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@ -356,43 +356,32 @@ pub fn connect_slices<T:Clone>(v: &[&[T]], sep: &T) -> ~[T] { v.connect_vec(sep)
pub trait VectorVector<T> {
// FIXME #5898: calling these .concat and .connect conflicts with
// StrVector::con{cat,nect}, since they have generic contents.
/// Flattens a vector of vectors of T into a single vector of T.
fn concat_vec(&self) -> ~[T];
/// Concatenate a vector of vectors, placing a given separator between each.
fn connect_vec(&self, sep: &T) -> ~[T];
}
impl<'self, T:Clone> VectorVector<T> for &'self [~[T]] {
/// Flattens a vector of slices of T into a single vector of T.
impl<'self, T: Clone, V: Vector<T>> VectorVector<T> for &'self [V] {
fn concat_vec(&self) -> ~[T] {
self.flat_map(|inner| (*inner).clone())
}
/// Concatenate a vector of vectors, placing a given separator between each.
fn connect_vec(&self, sep: &T) -> ~[T] {
let mut r = ~[];
let mut first = true;
for inner in self.iter() {
if first { first = false; } else { r.push((*sep).clone()); }
r.push_all((*inner).clone());
let size = self.iter().fold(0u, |acc, v| acc + v.as_slice().len());
let mut result = with_capacity(size);
for v in self.iter() {
result.push_all(v.as_slice())
}
r
}
}
impl<'self,T:Clone> VectorVector<T> for &'self [&'self [T]] {
/// Flattens a vector of slices of T into a single vector of T.
fn concat_vec(&self) -> ~[T] {
self.flat_map(|&inner| inner.to_owned())
result
}
/// Concatenate a vector of slices, placing a given separator between each.
fn connect_vec(&self, sep: &T) -> ~[T] {
let mut r = ~[];
let size = self.iter().fold(0u, |acc, v| acc + v.as_slice().len());
let mut result = with_capacity(size + self.len());
let mut first = true;
for &inner in self.iter() {
if first { first = false; } else { r.push((*sep).clone()); }
r.push_all(inner);
for v in self.iter() {
if first { first = false } else { result.push(sep.clone()) }
result.push_all(v.as_slice())
}
r
result
}
}