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core: Implement foldl/r without copying the accumulator

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This commit is contained in:
Brian Anderson 2012-02-12 03:04:33 -08:00
parent d679c0eb34
commit fde719f635
1 changed files with 18 additions and 12 deletions
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30
src/libcore/iter.rs
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@ -65,18 +65,18 @@ fn flat_map<A,B,IA:iterable<A>,IB:iterable<B>>(
}
}
fn foldl<A,B:copy,IA:iterable<A>>(self: IA, b0: B, blk: fn(B, A) -> B) -> B {
let b = b0;
fn foldl<A,B,IA:iterable<A>>(self: IA, +b0: B, blk: fn(-B, A) -> B) -> B {
let b <- b0;
self.iter {|a|
b = blk(b, a);
}
ret b;
}
fn foldr<A:copy,B:copy,IA:iterable<A>>(
self: IA, b0: B, blk: fn(A, B) -> B) -> B {
fn foldr<A:copy,B,IA:iterable<A>>(
self: IA, +b0: B, blk: fn(A, -B) -> B) -> B {
let b = b0;
let b <- b0;
reverse(self) {|a|
b = blk(a, b);
}
@ -111,10 +111,13 @@ fn repeat(times: uint, blk: fn()) {
}
fn min<A:copy,IA:iterable<A>>(self: IA) -> A {
alt foldl(self, none) {|a, b|
alt foldl::<A,option<A>,IA>(self, none) {|a, b|
alt a {
some(a) { some(math::min(a, b)) }
none { some(b) }
some(a_) if a_ < b {
// FIXME: Not sure if this is successfully optimized to a move
a
}
_ { some(b) }
}
} {
some(val) { val }
@ -123,10 +126,13 @@ fn min<A:copy,IA:iterable<A>>(self: IA) -> A {
}
fn max<A:copy,IA:iterable<A>>(self: IA) -> A {
alt foldl(self, none) {|a, b|
alt foldl::<A,option<A>,IA>(self, none) {|a, b|
alt a {
some(a) { some(math::max(a, b)) }
none { some(b) }
some(a_) if a_ > b {
// FIXME: Not sure if this is successfully optimized to a move
a
}
_ { some(b) }
}
} {
some(val) { val }
@ -252,7 +258,7 @@ fn test_count() {
#[test]
fn test_foldr() {
fn sub(&&a: int, &&b: int) -> int {
fn sub(&&a: int, -b: int) -> int {
a - b
}
let sum = foldr([1, 2, 3, 4], 0, sub);