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auto merge of #8526 : blake2-ppc/rust/either-result, r=catamorphism

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Retry of PR #8471

Replace the remaining functions marked for issue #8228 with similar functions that are iterator-based.

Change `either::{lefts, rights}` to be iterator-filtering instead of returning a vector.

Replace `map_vec`, `map_vec2`, `iter_vec2` in std::result with three functions:

* `result::collect` gathers `Iterator<Result<V, U>>` to `Result<~[V], U>`
* `result::fold` folds `Iterator<Result<T, E>>` to `Result<V, E>`
* `result::fold_` folds `Iterator<Result<T, E>>` to `Result<(), E>`
This commit is contained in:
bors 2013-08-16 01:56:16 -07:00
commit 72b50e729d
5 changed files with 130 additions and 103 deletions
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58
src/libstd/either.rs
View file

@ -16,7 +16,7 @@ use option::{Some, None};
use clone::Clone;
use container::Container;
use cmp::Eq;
use iterator::Iterator;
use iterator::{Iterator, FilterMap};
use result::Result;
use result;
use str::StrSlice;
@ -116,40 +116,44 @@ impl<L, R> Either<L, R> {
}
}
// FIXME: #8228 Replaceable by an external iterator?
/// Extracts from a vector of either all the left values
pub fn lefts<L: Clone, R>(eithers: &[Either<L, R>]) -> ~[L] {
do vec::build_sized(eithers.len()) |push| {
for elt in eithers.iter() {
match *elt {
Left(ref l) => { push((*l).clone()); }
_ => { /* fallthrough */ }
}
/// An iterator yielding the `Left` values of its source
pub type Lefts<L, R, Iter> = FilterMap<'static, Either<L, R>, L, Iter>;
/// An iterator yielding the `Right` values of its source
pub type Rights<L, R, Iter> = FilterMap<'static, Either<L, R>, R, Iter>;
/// Extracts all the left values
pub fn lefts<L, R, Iter: Iterator<Either<L, R>>>(eithers: Iter)
-> Lefts<L, R, Iter> {
do eithers.filter_map |elt| {
match elt {
Left(x) => Some(x),
_ => None,
}
}
}
// FIXME: #8228 Replaceable by an external iterator?
/// Extracts from a vector of either all the right values
pub fn rights<L, R: Clone>(eithers: &[Either<L, R>]) -> ~[R] {
do vec::build_sized(eithers.len()) |push| {
for elt in eithers.iter() {
match *elt {
Right(ref r) => { push((*r).clone()); }
_ => { /* fallthrough */ }
}
/// Extracts all the right values
pub fn rights<L, R, Iter: Iterator<Either<L, R>>>(eithers: Iter)
-> Rights<L, R, Iter> {
do eithers.filter_map |elt| {
match elt {
Right(x) => Some(x),
_ => None,
}
}
}
// FIXME: #8228 Replaceable by an external iterator?
/// Extracts from a vector of either all the left values and right values
///
/// Returns a structure containing a vector of left values and a vector of
/// right values.
pub fn partition<L, R>(eithers: ~[Either<L, R>]) -> (~[L], ~[R]) {
let mut lefts: ~[L] = ~[];
let mut rights: ~[R] = ~[];
let n_lefts = eithers.iter().count(|elt| elt.is_left());
let mut lefts = vec::with_capacity(n_lefts);
let mut rights = vec::with_capacity(eithers.len() - n_lefts);
for elt in eithers.move_iter() {
match elt {
Left(l) => lefts.push(l),
@ -182,42 +186,42 @@ mod tests {
#[test]
fn test_lefts() {
let input = ~[Left(10), Right(11), Left(12), Right(13), Left(14)];
let result = lefts(input);
let result = lefts(input.move_iter()).to_owned_vec();
assert_eq!(result, ~[10, 12, 14]);
}
#[test]
fn test_lefts_none() {
let input: ~[Either<int, int>] = ~[Right(10), Right(10)];
let result = lefts(input);
let result = lefts(input.move_iter()).to_owned_vec();
assert_eq!(result.len(), 0u);
}
#[test]
fn test_lefts_empty() {
let input: ~[Either<int, int>] = ~[];
let result = lefts(input);
let result = lefts(input.move_iter()).to_owned_vec();
assert_eq!(result.len(), 0u);
}
#[test]
fn test_rights() {
let input = ~[Left(10), Right(11), Left(12), Right(13), Left(14)];
let result = rights(input);
let result = rights(input.move_iter()).to_owned_vec();
assert_eq!(result, ~[11, 13]);
}
#[test]
fn test_rights_none() {
let input: ~[Either<int, int>] = ~[Left(10), Left(10)];
let result = rights(input);
let result = rights(input.move_iter()).to_owned_vec();
assert_eq!(result.len(), 0u);
}
#[test]
fn test_rights_empty() {
let input: ~[Either<int, int>] = ~[];
let result = rights(input);
let result = rights(input.move_iter()).to_owned_vec();
assert_eq!(result.len(), 0u);
}

139
src/libstd/result.rs
View file

@ -18,8 +18,7 @@ use either;
use iterator::Iterator;
use option::{None, Option, Some, OptionIterator};
use vec;
use vec::{OwnedVector, ImmutableVector};
use container::Container;
use vec::OwnedVector;
use to_str::ToStr;
use str::StrSlice;
@ -269,86 +268,76 @@ pub fn map_opt<T, U: ToStr, V>(o_t: &Option<T>,
}
}
// FIXME: #8228 Replaceable by an external iterator?
/// Maps each element in the vector `ts` using the operation `op`. Should an
/// error occur, no further mappings are performed and the error is returned.
/// Should no error occur, a vector containing the result of each map is
/// returned.
/// Takes each element in the iterator: if it is an error, no further
/// elements are taken, and the error is returned.
/// Should no error occur, a vector containing the values of each Result
/// is returned.
///
/// Here is an example which increments every integer in a vector,
/// checking for overflow:
///
/// fn inc_conditionally(x: uint) -> result<uint,str> {
/// fn inc_conditionally(x: uint) -> Result<uint, &'static str> {
/// if x == uint::max_value { return Err("overflow"); }
/// else { return Ok(x+1u); }
/// }
/// map(~[1u, 2u, 3u], inc_conditionally).chain {|incd|
/// assert!(incd == ~[2u, 3u, 4u]);
/// }
/// let v = [1u, 2, 3];
/// let res = collect(v.iter().map(|&x| inc_conditionally(x)));
/// assert!(res == Ok(~[2u, 3, 4]));
#[inline]
pub fn map_vec<T,U,V>(ts: &[T], op: &fn(&T) -> Result<V,U>)
-> Result<~[V],U> {
let mut vs: ~[V] = vec::with_capacity(ts.len());
for t in ts.iter() {
match op(t) {
Ok(v) => vs.push(v),
Err(u) => return Err(u)
pub fn collect<T, E, Iter: Iterator<Result<T, E>>>(mut iterator: Iter)
-> Result<~[T], E> {
let (lower, _) = iterator.size_hint();
let mut vs: ~[T] = vec::with_capacity(lower);
for t in iterator {
match t {
Ok(v) => vs.push(v),
Err(u) => return Err(u)
}
}
return Ok(vs);
Ok(vs)
}
// FIXME: #8228 Replaceable by an external iterator?
/// Same as map, but it operates over two parallel vectors.
/// Perform a fold operation over the result values from an iterator.
///
/// A precondition is used here to ensure that the vectors are the same
/// length. While we do not often use preconditions in the standard
/// library, a precondition is used here because result::t is generally
/// used in 'careful' code contexts where it is both appropriate and easy
/// to accommodate an error like the vectors being of different lengths.
/// If an `Err` is encountered, it is immediately returned.
/// Otherwise, the folded value is returned.
#[inline]
pub fn map_vec2<S, T, U: ToStr, V>(ss: &[S], ts: &[T],
op: &fn(&S,&T) -> Result<V,U>) -> Result<~[V],U> {
assert!(vec::same_length(ss, ts));
let n = ts.len();
let mut vs = vec::with_capacity(n);
let mut i = 0u;
while i < n {
match op(&ss[i],&ts[i]) {
Ok(v) => vs.push(v),
Err(u) => return Err(u)
pub fn fold<T, V, E,
Iter: Iterator<Result<T, E>>>(
mut iterator: Iter,
mut init: V,
f: &fn(V, T) -> V)
-> Result<V, E> {
for t in iterator {
match t {
Ok(v) => init = f(init, v),
Err(u) => return Err(u)
}
i += 1u;
}
return Ok(vs);
Ok(init)
}
// FIXME: #8228 Replaceable by an external iterator?
/// Applies op to the pairwise elements from `ss` and `ts`, aborting on
/// error. This could be implemented using `map_zip()` but it is more efficient
/// on its own as no result vector is built.
/// Perform a trivial fold operation over the result values
/// from an iterator.
///
/// If an `Err` is encountered, it is immediately returned.
/// Otherwise, a simple `Ok(())` is returned.
#[inline]
pub fn iter_vec2<S, T, U: ToStr>(ss: &[S], ts: &[T],
op: &fn(&S,&T) -> Result<(),U>) -> Result<(),U> {
assert!(vec::same_length(ss, ts));
let n = ts.len();
let mut i = 0u;
while i < n {
match op(&ss[i],&ts[i]) {
Ok(()) => (),
Err(u) => return Err(u)
}
i += 1u;
}
return Ok(());
pub fn fold_<T, E, Iter: Iterator<Result<T, E>>>(
iterator: Iter)
-> Result<(), E> {
fold(iterator, (), |_, _| ())
}
#[cfg(test)]
mod tests {
use super::*;
use either;
use iterator::range;
use str::OwnedStr;
use vec::ImmutableVector;
pub fn op1() -> Result<int, ~str> { Ok(666) }
@ -431,4 +420,44 @@ mod tests {
assert_eq!(r.to_either(), either::Right(100));
assert_eq!(err.to_either(), either::Left(404));
}
#[test]
fn test_collect() {
assert_eq!(collect(range(0, 0)
.map(|_| Ok::<int, ()>(0))),
Ok(~[]));
assert_eq!(collect(range(0, 3)
.map(|x| Ok::<int, ()>(x))),
Ok(~[0, 1, 2]));
assert_eq!(collect(range(0, 3)
.map(|x| if x > 1 { Err(x) } else { Ok(x) })),
Err(2));
// test that it does not take more elements than it needs
let functions = [|| Ok(()), || Err(1), || fail!()];
assert_eq!(collect(functions.iter().map(|f| (*f)())),
Err(1));
}
#[test]
fn test_fold() {
assert_eq!(fold_(range(0, 0)
.map(|_| Ok::<(), ()>(()))),
Ok(()));
assert_eq!(fold(range(0, 3)
.map(|x| Ok::<int, ()>(x)),
0, |a, b| a + b),
Ok(3));
assert_eq!(fold_(range(0, 3)
.map(|x| if x > 1 { Err(x) } else { Ok(()) })),
Err(2));
// test that it does not take more elements than it needs
let functions = [|| Ok(()), || Err(1), || fail!()];
assert_eq!(fold_(functions.iter()
.map(|f| (*f)())),
Err(1));
}
}