1.0.0[][src]Trait std::iter::FromIterator

pub trait FromIterator<A> {
    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.

FromIterator's from_iter is rarely called explicitly, and is instead used through Iterator's collect method. See collect's documentation for more examples.

See also: IntoIterator.

Examples

Basic usage:

use std::iter::FromIterator;

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]);Run

Using 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]);Run

Implementing FromIterator for your type:

use std::iter::FromIterator;

// 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]);Run

Required Methods

Creates a value from an iterator.

See the module-level documentation for more.

Examples

Basic usage:

use std::iter::FromIterator;

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]);Run

Implementors

impl FromIterator<char> for String
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impl FromIterator<()> for ()
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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());Run

impl FromIterator<String> for String
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impl<'a> FromIterator<&'a char> for String
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impl<'a> FromIterator<&'a str> for String
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impl<'a> FromIterator<Cow<'a, str>> for String
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impl<'a> FromIterator<char> for Cow<'a, str>
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impl<'a> FromIterator<String> for Cow<'a, str>
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impl<'a, 'b> FromIterator<&'b str> for Cow<'a, str>
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impl<'a, T> FromIterator<T> for Cow<'a, [T]> where
    T: Clone
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impl<A> FromIterator<A> for Box<[A]>
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impl<A> FromIterator<A> for VecDeque<A>
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impl<A, E, V> FromIterator<Result<A, E>> for Result<V, E> where
    V: FromIterator<A>, 
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Takes each element in the Iterator: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, a container with the values of each Result is returned.

Here is an example which increments every integer in a vector, checking for overflow:

let v = vec![1, 2];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
    x.checked_add(1).ok_or("Overflow!")
).collect();
assert!(res == Ok(vec![2, 3]));Run

impl<A, V> FromIterator<Option<A>> for Option<V> where
    V: FromIterator<A>, 
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Takes each element in the Iterator: if it is None, no further elements are taken, and the None is returned. Should no None occur, a container with the values of each Option is returned.

Here is an example which increments every integer in a vector, checking for overflow:

use std::u16;

let v = vec![1, 2];
let res: Option<Vec<u16>> = v.iter().map(|&x: &u16|
    if x == u16::MAX { None }
    else { Some(x + 1) }
).collect();
assert!(res == Some(vec![2, 3]));Run

impl<K, V> FromIterator<(K, V)> for BTreeMap<K, V> where
    K: Ord
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impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S> where
    K: Eq + Hash,
    S: BuildHasher + Default
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impl<P: AsRef<Path>> FromIterator<P> for PathBuf
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impl<T> FromIterator<T> for BinaryHeap<T> where
    T: Ord
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impl<T> FromIterator<T> for BTreeSet<T> where
    T: Ord
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impl<T> FromIterator<T> for LinkedList<T>
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impl<T> FromIterator<T> for Vec<T>
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impl<T, S> FromIterator<T> for HashSet<T, S> where
    T: Eq + Hash,
    S: BuildHasher + Default
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