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, Flatten, FlatMap, Fuse};
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 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 }
+ self.map(f).flatten()
+ }
+
+ /// 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");
+ /// ```
+ #[inline]
+ #[unstable(feature = "iterator_flatten", issue = "0")]
+ fn flatten(self) -> Flatten<Self, <Self::Item as IntoIterator>::IntoIter>
+ where Self: Sized, Self::Item: IntoIterator {
+ Flatten { iter: self, frontiter: None, backiter: None }
}
/// Creates an iterator which ends after the first [`None`].
/// An iterator that maps each element to an iterator, and yields the elements
/// of the produced iterators.
///
-/// This `struct` is created by the [`flat_map`] method on [`Iterator`]. See its
+/// This `type` is created by the [`flat_map`] method on [`Iterator`]. See its
/// documentation for more.
///
/// [`flat_map`]: trait.Iterator.html#method.flat_map
/// [`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>,
-}
+type FlatMap<I, U, F> = Flatten<Map<I, F>, <U as IntoIterator>::IntoIter>;
-#[stable(feature = "core_impl_debug", since = "1.9.0")]
-impl<I: fmt::Debug, U: IntoIterator, F> fmt::Debug for FlatMap<I, U, F>
- 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()
- }
+/// 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 = "0")]
+#[derive(Clone, Debug)]
+pub struct Flatten<I, U> {
+ iter: I,
+ frontiter: Option<U>,
+ backiter: Option<U>,
}
-#[stable(feature = "rust1", since = "1.0.0")]
-impl<I: Iterator, U: IntoIterator, F> Iterator for FlatMap<I, U, F>
- where F: FnMut(I::Item) -> U,
+#[unstable(feature = "iterator_flatten", issue = "0")]
+impl<I: Iterator, U: Iterator> Iterator for Flatten<I, U>
+ where I::Item: IntoIterator<IntoIter = U, Item = U::Item>
{
type Item = U::Item;
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
+#[unstable(feature = "iterator_flatten", issue = "0")]
+impl<I, U> DoubleEndedIterator for Flatten<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 {}
+#[unstable(feature = "fused", issue = "0")]
+impl<I: FusedIterator, U: Iterator> FusedIterator for Flatten<I, U>
+ where I::Item: IntoIterator<IntoIter = U, Item = U::Item> {}
/// An iterator that yields `None` forever after the underlying iterator
/// yields `None` once.
projects / rust.git / commitdiff