Trait std::iter::FromIterator
pub trait FromIterator<A>: Sized {
// Required method
fn from_iter<T>(iter: T) -> Self
where T: IntoIterator<Item = A>;
}Conversion from an Iterator.
By implementing FromIterator for a type, you define how it will be created from an iterator. This is common for types which describe a collection of some kind.
If you want to create a collection from the contents of an iterator, the Iterator::collect() method is preferred. However, when you need to specify the container type, FromIterator::from_iter() can be more readable than using a turbofish (e.g. ::<Vec<_>>()). See the Iterator::collect() documentation for more examples of its use.
See also: IntoIterator.
Examples
Basic usage:
let five_fives = std::iter::repeat(5).take(5);
let v = Vec::from_iter(five_fives);
assert_eq!(v, vec![5, 5, 5, 5, 5]);Using Iterator::collect() to implicitly use FromIterator:
let five_fives = std::iter::repeat(5).take(5);
let v: Vec<i32> = five_fives.collect();
assert_eq!(v, vec![5, 5, 5, 5, 5]);Using FromIterator::from_iter() as a more readable alternative to Iterator::collect():
use std::collections::VecDeque;
let first = (0..10).collect::<VecDeque<i32>>();
let second = VecDeque::from_iter(0..10);
assert_eq!(first, second);Implementing FromIterator for your type:
// A sample collection, that's just a wrapper over Vec<T>
#[derive(Debug)]
struct MyCollection(Vec<i32>);
// Let's give it some methods so we can create one and add things
// to it.
impl MyCollection {
fn new() -> MyCollection {
MyCollection(Vec::new())
}
fn add(&mut self, elem: i32) {
self.0.push(elem);
}
}
// and we'll implement FromIterator
impl FromIterator<i32> for MyCollection {
fn from_iter<I: IntoIterator<Item=i32>>(iter: I) -> Self {
let mut c = MyCollection::new();
for i in iter {
c.add(i);
}
c
}
}
// Now we can make a new iterator...
let iter = (0..5).into_iter();
// ... and make a MyCollection out of it
let c = MyCollection::from_iter(iter);
assert_eq!(c.0, vec![0, 1, 2, 3, 4]);
// collect works too!
let iter = (0..5).into_iter();
let c: MyCollection = iter.collect();
assert_eq!(c.0, vec![0, 1, 2, 3, 4]);Required Methods
fn from_iter<T>(iter: T) -> Self
where
T: IntoIterator<Item = A>,Creates a value from an iterator.
See the module-level documentation for more.
Examples
let five_fives = std::iter::repeat(5).take(5);
let v = Vec::from_iter(five_fives);
assert_eq!(v, vec![5, 5, 5, 5, 5]);Object Safety
This trait is not object safe.
Implementors
impl FromIterator<char> for Stringimpl FromIterator<()> for ()Collapses all unit items from an iterator into one.
This is more useful when combined with higher-level abstractions, like collecting to a Result<(), E> where you only care about errors:
use std::io::*;
let data = vec![1, 2, 3, 4, 5];
let res: Result<()> = data.iter()
.map(|x| writeln!(stdout(), "{x}"))
.collect();
assert!(res.is_ok());impl FromIterator<Box<str>> for Stringimpl FromIterator<OsString> for OsStringimpl FromIterator<String> for Stringimpl<'a> FromIterator<&'a char> for Stringimpl<'a> FromIterator<&'a str> for Stringimpl<'a> FromIterator<&'a OsStr> for OsStringimpl<'a> FromIterator<Cow<'a, str>> for Stringimpl<'a> FromIterator<Cow<'a, OsStr>> for OsStringimpl<'a> FromIterator<char> for Cow<'a, str>impl<'a> FromIterator<String> for Cow<'a, str>impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>impl<'a, T> FromIterator<T> for Cow<'a, [T]>
where
T: Clone,impl<A, E, V> FromIterator<Result<A, E>> for Result<V, E>
where
V: FromIterator<A>,impl<A, V> FromIterator<Option<A>> for Option<V>
where
V: FromIterator<A>,impl<I> FromIterator<I> for Box<[I]>impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V>
where
K: Ord,impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
where
K: Eq + Hash,
S: BuildHasher + Default,impl<P: AsRef<Path>> FromIterator<P> for PathBufimpl<T> FromIterator<T> for BTreeSet<T>
where
T: Ord,impl<T> FromIterator<T> for BinaryHeap<T>
where
T: Ord,impl<T> FromIterator<T> for LinkedList<T>impl<T> FromIterator<T> for VecDeque<T>impl<T> FromIterator<T> for Rc<[T]>impl<T> FromIterator<T> for Arc<[T]>impl<T> FromIterator<T> for Vec<T>impl<T, S> FromIterator<T> for HashSet<T, S>
where
T: Eq + Hash,
S: BuildHasher + Default,© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/iter/trait.FromIterator.html