use ops::Try;
use super::{AlwaysOk, LoopState};
-use super::{Chain, Cycle, Cloned, Enumerate, Filter, FilterMap, FlatMap, Fuse};
+use super::{Chain, Cycle, Cloned, Enumerate, Filter, FilterMap, Fuse};
+use super::{Flatten, FlatMap, flatten_compat};
use super::{Inspect, Map, Peekable, Scan, Skip, SkipWhile, StepBy, Take, TakeWhile, Rev};
use super::{Zip, Sum, Product};
use super::{ChainState, FromIterator, ZipImpl};
/// an extra layer of indirection. `flat_map()` will remove this extra layer
/// on its own.
///
+ /// You can think of [`flat_map(f)`][flat_map] as the semantic equivalent
+ /// of [`map`]ping, and then [`flatten`]ing as in `map(f).flatten()`.
+ ///
/// Another way of thinking about `flat_map()`: [`map`]'s closure returns
/// one item for each element, and `flat_map()`'s closure returns an
/// iterator for each element.
///
/// [`map`]: #method.map
+ /// [`flatten`]: #method.flatten
///
/// # Examples
///
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>
where Self: Sized, U: IntoIterator, F: FnMut(Self::Item) -> U,
{
- FlatMap{iter: self, f: f, frontiter: None, backiter: None }
+ FlatMap { inner: flatten_compat(self.map(f)) }
+ }
+
+ /// Creates an iterator that flattens nested structure.
+ ///
+ /// This is useful when you have an iterator of iterators or an iterator of
+ /// things that can be turned into iterators and you want to remove one
+ /// level of indirection.
+ ///
+ /// # Examples
+ ///
+ /// Basic usage:
+ ///
+ /// ```
+ /// #![feature(iterator_flatten)]
+ ///
+ /// let data = vec![vec![1, 2, 3, 4], vec![5, 6]];
+ /// let flattened = data.into_iter().flatten().collect::<Vec<u8>>();
+ /// assert_eq!(flattened, &[1, 2, 3, 4, 5, 6]);
+ /// ```
+ ///
+ /// Mapping and then flattening:
+ ///
+ /// ```
+ /// #![feature(iterator_flatten)]
+ ///
+ /// let words = ["alpha", "beta", "gamma"];
+ ///
+ /// // chars() returns an iterator
+ /// let merged: String = words.iter()
+ /// .map(|s| s.chars())
+ /// .flatten()
+ /// .collect();
+ /// assert_eq!(merged, "alphabetagamma");
+ /// ```
+ ///
+ /// You can also rewrite this in terms of [`flat_map()`] which is preferable
+ /// in this case since that conveys intent clearer:
+ ///
+ /// ```
+ /// let words = ["alpha", "beta", "gamma"];
+ ///
+ /// // chars() returns an iterator
+ /// let merged: String = words.iter()
+ /// .flat_map(|s| s.chars())
+ /// .collect();
+ /// assert_eq!(merged, "alphabetagamma");
+ /// ```
+ ///
+ /// Flattening once only removes one level of nesting:
+ ///
+ /// ```
+ /// #![feature(iterator_flatten)]
+ ///
+ /// let d3 = [[[1, 2], [3, 4]], [[5, 6], [7, 8]]];
+ ///
+ /// let d2 = d3.iter().flatten().collect::<Vec<_>>();
+ /// assert_eq!(d2, [&[1, 2], &[3, 4], &[5, 6], &[7, 8]]);
+ ///
+ /// let d1 = d3.iter().flatten().flatten().collect::<Vec<_>>();
+ /// assert_eq!(d1, [&1, &2, &3, &4, &5, &6, &7, &8]);
+ /// ```
+ ///
+ /// Here we see that `flatten()` does not perform a "deep" flatten.
+ /// Instead, only one level of nesting is removed. That is, if you
+ /// `flatten()` a three-dimensional array the result will be
+ /// two-dimensional and not one-dimensional. To get a one-dimensional
+ /// structure, you have to `flatten()` again.
+ #[inline]
+ #[unstable(feature = "iterator_flatten", issue = "48213")]
+ fn flatten(self) -> Flatten<Self>
+ where Self: Sized, Self::Item: IntoIterator {
+ Flatten { inner: flatten_compat(self) }
}
/// Creates an iterator which ends after the first [`None`].
/// [`Iterator`]: trait.Iterator.html
#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
#[stable(feature = "rust1", since = "1.0.0")]
-#[derive(Clone)]
pub struct FlatMap<I, U: IntoIterator, F> {
- iter: I,
- f: F,
- frontiter: Option<U::IntoIter>,
- backiter: Option<U::IntoIter>,
+ inner: FlattenCompat<Map<I, F>, <U as IntoIterator>::IntoIter>
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<I: Clone, U: Clone + IntoIterator, F: Clone> Clone for FlatMap<I, U, F>
+ where <U as IntoIterator>::IntoIter: Clone
+{
+ fn clone(&self) -> Self { FlatMap { inner: self.inner.clone() } }
}
#[stable(feature = "core_impl_debug", since = "1.9.0")]
where U::IntoIter: fmt::Debug
{
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
- f.debug_struct("FlatMap")
- .field("iter", &self.iter)
- .field("frontiter", &self.frontiter)
- .field("backiter", &self.backiter)
- .finish()
+ f.debug_struct("FlatMap").field("inner", &self.inner).finish()
}
}
{
type Item = U::Item;
+ #[inline]
+ fn next(&mut self) -> Option<U::Item> { self.inner.next() }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
+
+ #[inline]
+ fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
+ Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
+ {
+ self.inner.try_fold(init, fold)
+ }
+
+ #[inline]
+ fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+ where Fold: FnMut(Acc, Self::Item) -> Acc,
+ {
+ self.inner.fold(init, fold)
+ }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F>
+ where F: FnMut(I::Item) -> U,
+ U: IntoIterator,
+ U::IntoIter: DoubleEndedIterator
+{
+ #[inline]
+ fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
+
+ #[inline]
+ fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
+ Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
+ {
+ self.inner.try_rfold(init, fold)
+ }
+
+ #[inline]
+ fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+ where Fold: FnMut(Acc, Self::Item) -> Acc,
+ {
+ self.inner.rfold(init, fold)
+ }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<I, U, F> FusedIterator for FlatMap<I, U, F>
+ where I: FusedIterator, U: IntoIterator, F: FnMut(I::Item) -> U {}
+
+/// An iterator that flattens one level of nesting in an iterator of things
+/// that can be turned into iterators.
+///
+/// This `struct` is created by the [`flatten`] method on [`Iterator`]. See its
+/// documentation for more.
+///
+/// [`flatten`]: trait.Iterator.html#method.flatten
+/// [`Iterator`]: trait.Iterator.html
+#[must_use = "iterator adaptors are lazy and do nothing unless consumed"]
+#[unstable(feature = "iterator_flatten", issue = "48213")]
+pub struct Flatten<I: Iterator>
+where I::Item: IntoIterator {
+ inner: FlattenCompat<I, <I::Item as IntoIterator>::IntoIter>,
+}
+
+#[unstable(feature = "iterator_flatten", issue = "48213")]
+impl<I, U> fmt::Debug for Flatten<I>
+ where I: Iterator + fmt::Debug, U: Iterator + fmt::Debug,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
+{
+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+ f.debug_struct("Flatten").field("inner", &self.inner).finish()
+ }
+}
+
+#[unstable(feature = "iterator_flatten", issue = "48213")]
+impl<I, U> Clone for Flatten<I>
+ where I: Iterator + Clone, U: Iterator + Clone,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item>,
+{
+ fn clone(&self) -> Self { Flatten { inner: self.inner.clone() } }
+}
+
+#[unstable(feature = "iterator_flatten", issue = "48213")]
+impl<I, U> Iterator for Flatten<I>
+ where I: Iterator, U: Iterator,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item>
+{
+ type Item = U::Item;
+
+ #[inline]
+ fn next(&mut self) -> Option<U::Item> { self.inner.next() }
+
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
+
+ #[inline]
+ fn try_fold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
+ Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
+ {
+ self.inner.try_fold(init, fold)
+ }
+
+ #[inline]
+ fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+ where Fold: FnMut(Acc, Self::Item) -> Acc,
+ {
+ self.inner.fold(init, fold)
+ }
+}
+
+#[unstable(feature = "iterator_flatten", issue = "48213")]
+impl<I, U> DoubleEndedIterator for Flatten<I>
+ where I: DoubleEndedIterator, U: DoubleEndedIterator,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item>
+{
+ #[inline]
+ fn next_back(&mut self) -> Option<U::Item> { self.inner.next_back() }
+
+ #[inline]
+ fn try_rfold<Acc, Fold, R>(&mut self, init: Acc, fold: Fold) -> R where
+ Self: Sized, Fold: FnMut(Acc, Self::Item) -> R, R: Try<Ok=Acc>
+ {
+ self.inner.try_rfold(init, fold)
+ }
+
+ #[inline]
+ fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+ where Fold: FnMut(Acc, Self::Item) -> Acc,
+ {
+ self.inner.rfold(init, fold)
+ }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<I, U> FusedIterator for Flatten<I>
+ where I: FusedIterator, U: Iterator,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item> {}
+
+/// Adapts an iterator by flattening it, for use in `flatten()` and `flat_map()`.
+fn flatten_compat<I, U>(iter: I) -> FlattenCompat<I, U> {
+ FlattenCompat { iter, frontiter: None, backiter: None }
+}
+
+/// Real logic of both `Flatten` and `FlatMap` which simply delegate to
+/// this type.
+#[derive(Clone, Debug)]
+struct FlattenCompat<I, U> {
+ iter: I,
+ frontiter: Option<U>,
+ backiter: Option<U>,
+}
+
+impl<I, U> Iterator for FlattenCompat<I, U>
+ where I: Iterator, U: Iterator,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item>
+{
+ type Item = U::Item;
+
#[inline]
fn next(&mut self) -> Option<U::Item> {
loop {
if let Some(ref mut inner) = self.frontiter {
- if let Some(x) = inner.by_ref().next() {
- return Some(x)
- }
+ if let elt@Some(_) = inner.next() { return elt }
}
- match self.iter.next().map(&mut self.f) {
+ match self.iter.next() {
None => return self.backiter.as_mut().and_then(|it| it.next()),
- next => self.frontiter = next.map(IntoIterator::into_iter),
+ Some(inner) => self.frontiter = Some(inner.into_iter()),
}
}
}
self.frontiter = None;
{
- let f = &mut self.f;
let frontiter = &mut self.frontiter;
init = self.iter.try_fold(init, |acc, x| {
- let mut mid = f(x).into_iter();
+ let mut mid = x.into_iter();
let r = mid.try_fold(acc, &mut fold);
*frontiter = Some(mid);
r
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.frontiter.into_iter()
- .chain(self.iter.map(self.f).map(U::into_iter))
+ .chain(self.iter.map(IntoIterator::into_iter))
.chain(self.backiter)
.fold(init, |acc, iter| iter.fold(acc, &mut fold))
}
}
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F> where
- F: FnMut(I::Item) -> U,
- U: IntoIterator,
- U::IntoIter: DoubleEndedIterator
+impl<I, U> DoubleEndedIterator for FlattenCompat<I, U>
+ where I: DoubleEndedIterator, U: DoubleEndedIterator,
+ I::Item: IntoIterator<IntoIter = U, Item = U::Item>
{
#[inline]
fn next_back(&mut self) -> Option<U::Item> {
loop {
if let Some(ref mut inner) = self.backiter {
- if let Some(y) = inner.next_back() {
- return Some(y)
- }
+ if let elt@Some(_) = inner.next_back() { return elt }
}
- match self.iter.next_back().map(&mut self.f) {
+ match self.iter.next_back() {
None => return self.frontiter.as_mut().and_then(|it| it.next_back()),
next => self.backiter = next.map(IntoIterator::into_iter),
}
self.backiter = None;
{
- let f = &mut self.f;
let backiter = &mut self.backiter;
init = self.iter.try_rfold(init, |acc, x| {
- let mut mid = f(x).into_iter();
+ let mut mid = x.into_iter();
let r = mid.try_rfold(acc, &mut fold);
*backiter = Some(mid);
r
where Fold: FnMut(Acc, Self::Item) -> Acc,
{
self.frontiter.into_iter()
- .chain(self.iter.map(self.f).map(U::into_iter))
+ .chain(self.iter.map(IntoIterator::into_iter))
.chain(self.backiter)
.rfold(init, |acc, iter| iter.rfold(acc, &mut fold))
}
}
-#[unstable(feature = "fused", issue = "35602")]
-impl<I, U, F> FusedIterator for FlatMap<I, U, F>
- where I: FusedIterator, U: IntoIterator, F: FnMut(I::Item) -> U {}
-
/// An iterator that yields `None` forever after the underlying iterator
/// yields `None` once.
///
assert_eq!(i, 0);
}
+#[test]
+fn test_iterator_flatten() {
+ let xs = [0, 3, 6];
+ let ys = [0, 1, 2, 3, 4, 5, 6, 7, 8];
+ let it = xs.iter().map(|&x| (x..).step_by(1).take(3)).flatten();
+ let mut i = 0;
+ for x in it {
+ assert_eq!(x, ys[i]);
+ i += 1;
+ }
+ assert_eq!(i, ys.len());
+}
+
+/// Test `Flatten::fold` with items already picked off the front and back,
+/// to make sure all parts of the `Flatten` are folded correctly.
+#[test]
+fn test_iterator_flatten_fold() {
+ let xs = [0, 3, 6];
+ let ys = [1, 2, 3, 4, 5, 6, 7];
+ let mut it = xs.iter().map(|&x| x..x+3).flatten();
+ assert_eq!(it.next(), Some(0));
+ assert_eq!(it.next_back(), Some(8));
+ let i = it.fold(0, |i, x| {
+ assert_eq!(x, ys[i]);
+ i + 1
+ });
+ assert_eq!(i, ys.len());
+
+ let mut it = xs.iter().map(|&x| x..x+3).flatten();
+ assert_eq!(it.next(), Some(0));
+ assert_eq!(it.next_back(), Some(8));
+ let i = it.rfold(ys.len(), |i, x| {
+ assert_eq!(x, ys[i - 1]);
+ i - 1
+ });
+ assert_eq!(i, 0);
+}
+
#[test]
fn test_inspect() {
let xs = [1, 2, 3, 4];
assert_eq!(it.next_back(), None);
}
+#[test]
+fn test_double_ended_flatten() {
+ let u = [0,1];
+ let v = [5,6,7,8];
+ let mut it = u.iter().map(|x| &v[*x..v.len()]).flatten();
+ assert_eq!(it.next_back().unwrap(), &8);
+ assert_eq!(it.next().unwrap(), &5);
+ assert_eq!(it.next_back().unwrap(), &7);
+ assert_eq!(it.next_back().unwrap(), &6);
+ assert_eq!(it.next_back().unwrap(), &8);
+ assert_eq!(it.next().unwrap(), &6);
+ assert_eq!(it.next_back().unwrap(), &7);
+ assert_eq!(it.next_back(), None);
+ assert_eq!(it.next(), None);
+ assert_eq!(it.next_back(), None);
+}
+
#[test]
fn test_double_ended_range() {
assert_eq!((11..14).rev().collect::<Vec<_>>(), [13, 12, 11]);
assert_eq!(iter.try_rfold(0, i8::checked_add), None);
assert_eq!(iter.next_back(), Some(35));
}
+
+#[test]
+fn test_flatten_try_folds() {
+ let f = &|acc, x| i32::checked_add(acc*2/3, x);
+ let mr = &|x| (5*x)..(5*x + 5);
+ assert_eq!((0..10).map(mr).flatten().try_fold(7, f), (0..50).try_fold(7, f));
+ assert_eq!((0..10).map(mr).flatten().try_rfold(7, f), (0..50).try_rfold(7, f));
+ let mut iter = (0..10).map(mr).flatten();
+ iter.next(); iter.next_back(); // have front and back iters in progress
+ assert_eq!(iter.try_rfold(7, f), (1..49).try_rfold(7, f));
+
+ let mut iter = (0..10).map(|x| (4*x)..(4*x + 4)).flatten();
+ assert_eq!(iter.try_fold(0, i8::checked_add), None);
+ assert_eq!(iter.next(), Some(17));
+ assert_eq!(iter.try_rfold(0, i8::checked_add), None);
+ assert_eq!(iter.next_back(), Some(35));
+}
+
+#[test]
+fn test_functor_laws() {
+ // identity:
+ fn identity<T>(x: T) -> T { x }
+ assert_eq!((0..10).map(identity).sum::<usize>(), (0..10).sum());
+
+ // composition:
+ fn f(x: usize) -> usize { x + 3 }
+ fn g(x: usize) -> usize { x * 2 }
+ fn h(x: usize) -> usize { g(f(x)) }
+ assert_eq!((0..10).map(f).map(g).sum::<usize>(), (0..10).map(h).sum());
+}
+
+#[test]
+fn test_monad_laws_left_identity() {
+ fn f(x: usize) -> impl Iterator<Item = usize> {
+ (0..10).map(move |y| x * y)
+ }
+ assert_eq!(once(42).flat_map(f.clone()).sum::<usize>(), f(42).sum());
+}
+
+#[test]
+fn test_monad_laws_right_identity() {
+ assert_eq!((0..10).flat_map(|x| once(x)).sum::<usize>(), (0..10).sum());
+}
+
+#[test]
+fn test_monad_laws_associativity() {
+ fn f(x: usize) -> impl Iterator<Item = usize> { 0..x }
+ fn g(x: usize) -> impl Iterator<Item = usize> { (0..x).rev() }
+ assert_eq!((0..10).flat_map(f).flat_map(g).sum::<usize>(),
+ (0..10).flat_map(|x| f(x).flat_map(g)).sum::<usize>());
+}
projects / rust.git / commitdiff