rust/src/libstd/either.rs

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// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! A type that represents one of two alternatives
#[allow(missing_doc)];
use container::Container;
use cmp::Eq;
use kinds::Copy;
use old_iter::BaseIter;
use result::Result;
use result;
use vec;
use vec::OwnedVector;
/// The either type
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#[deriving(Clone, Eq)]
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pub enum Either<T, U> {
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Left(T),
Right(U)
}
/// Applies a function based on the given either value
///
/// If `value` is left(T) then `f_left` is applied to its contents, if
/// `value` is right(U) then `f_right` is applied to its contents, and the
/// result is returned.
#[inline(always)]
pub fn either<T, U, V>(f_left: &fn(&T) -> V,
f_right: &fn(&U) -> V, value: &Either<T, U>) -> V {
match *value {
Left(ref l) => f_left(l),
Right(ref r) => f_right(r)
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}
}
/// Extracts from a vector of either all the left values
pub fn lefts<T:Copy,U>(eithers: &[Either<T, U>]) -> ~[T] {
do vec::build_sized(eithers.len()) |push| {
for eithers.each |elt| {
match *elt {
Left(ref l) => { push(*l); }
_ => { /* fallthrough */ }
}
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}
}
}
/// Extracts from a vector of either all the right values
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pub fn rights<T, U: Copy>(eithers: &[Either<T, U>]) -> ~[U] {
do vec::build_sized(eithers.len()) |push| {
for eithers.each |elt| {
match *elt {
Right(ref r) => { push(*r); }
_ => { /* fallthrough */ }
}
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}
}
}
/// 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<T, U>(eithers: ~[Either<T, U>]) -> (~[T], ~[U]) {
let mut lefts: ~[T] = ~[];
let mut rights: ~[U] = ~[];
do vec::consume(eithers) |_i, elt| {
match elt {
Left(l) => lefts.push(l),
Right(r) => rights.push(r)
}
}
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return (lefts, rights);
}
/// Flips between left and right of a given either
#[inline(always)]
pub fn flip<T, U>(eith: Either<T, U>) -> Either<U, T> {
match eith {
Right(r) => Left(r),
Left(l) => Right(l)
}
}
/// Converts either::t to a result::t
///
/// Converts an `either` type to a `result` type, making the "right" choice
/// an ok result, and the "left" choice a fail
#[inline(always)]
pub fn to_result<T, U>(eith: Either<T, U>) -> Result<U, T> {
match eith {
Right(r) => result::Ok(r),
Left(l) => result::Err(l)
}
}
/// Checks whether the given value is a left
#[inline(always)]
pub fn is_left<T, U>(eith: &Either<T, U>) -> bool {
match *eith {
Left(_) => true,
_ => false
}
}
/// Checks whether the given value is a right
#[inline(always)]
pub fn is_right<T, U>(eith: &Either<T, U>) -> bool {
match *eith {
Right(_) => true,
_ => false
}
}
/// Retrieves the value in the left branch. Fails if the either is Right.
#[inline(always)]
pub fn unwrap_left<T,U>(eith: Either<T,U>) -> T {
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match eith {
Left(x) => x,
Right(_) => fail!("either::unwrap_left Right")
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}
}
/// Retrieves the value in the right branch. Fails if the either is Left.
#[inline(always)]
pub fn unwrap_right<T,U>(eith: Either<T,U>) -> U {
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match eith {
Right(x) => x,
Left(_) => fail!("either::unwrap_right Left")
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}
}
impl<T, U> Either<T, U> {
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#[inline(always)]
pub fn either<V>(&self, f_left: &fn(&T) -> V, f_right: &fn(&U) -> V) -> V {
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either(f_left, f_right, self)
}
#[inline(always)]
pub fn flip(self) -> Either<U, T> { flip(self) }
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#[inline(always)]
pub fn to_result(self) -> Result<U, T> { to_result(self) }
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#[inline(always)]
pub fn is_left(&self) -> bool { is_left(self) }
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#[inline(always)]
pub fn is_right(&self) -> bool { is_right(self) }
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#[inline(always)]
pub fn unwrap_left(self) -> T { unwrap_left(self) }
#[inline(always)]
pub fn unwrap_right(self) -> U { unwrap_right(self) }
}
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#[test]
fn test_either_left() {
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let val = Left(10);
fn f_left(x: &int) -> bool { *x == 10 }
fn f_right(_x: &uint) -> bool { false }
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assert!((either(f_left, f_right, &val)));
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}
#[test]
fn test_either_right() {
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let val = Right(10u);
fn f_left(_x: &int) -> bool { false }
fn f_right(x: &uint) -> bool { *x == 10u }
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assert!((either(f_left, f_right, &val)));
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}
#[test]
fn test_lefts() {
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let input = ~[Left(10), Right(11), Left(12), Right(13), Left(14)];
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let result = lefts(input);
assert_eq!(result, ~[10, 12, 14]);
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}
#[test]
fn test_lefts_none() {
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let input: ~[Either<int, int>] = ~[Right(10), Right(10)];
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let result = lefts(input);
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assert_eq!(result.len(), 0u);
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}
#[test]
fn test_lefts_empty() {
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let input: ~[Either<int, int>] = ~[];
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let result = lefts(input);
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assert_eq!(result.len(), 0u);
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}
#[test]
fn test_rights() {
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let input = ~[Left(10), Right(11), Left(12), Right(13), Left(14)];
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let result = rights(input);
assert_eq!(result, ~[11, 13]);
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}
#[test]
fn test_rights_none() {
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let input: ~[Either<int, int>] = ~[Left(10), Left(10)];
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let result = rights(input);
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assert_eq!(result.len(), 0u);
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}
#[test]
fn test_rights_empty() {
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let input: ~[Either<int, int>] = ~[];
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let result = rights(input);
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assert_eq!(result.len(), 0u);
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}
#[test]
fn test_partition() {
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let input = ~[Left(10), Right(11), Left(12), Right(13), Left(14)];
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let (lefts, rights) = partition(input);
assert_eq!(lefts[0], 10);
assert_eq!(lefts[1], 12);
assert_eq!(lefts[2], 14);
assert_eq!(rights[0], 11);
assert_eq!(rights[1], 13);
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}
#[test]
fn test_partition_no_lefts() {
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let input: ~[Either<int, int>] = ~[Right(10), Right(11)];
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let (lefts, rights) = partition(input);
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assert_eq!(lefts.len(), 0u);
assert_eq!(rights.len(), 2u);
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}
#[test]
fn test_partition_no_rights() {
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let input: ~[Either<int, int>] = ~[Left(10), Left(11)];
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let (lefts, rights) = partition(input);
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assert_eq!(lefts.len(), 2u);
assert_eq!(rights.len(), 0u);
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}
#[test]
fn test_partition_empty() {
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let input: ~[Either<int, int>] = ~[];
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let (lefts, rights) = partition(input);
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assert_eq!(lefts.len(), 0u);
assert_eq!(rights.len(), 0u);
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}