# Function core::iter::repeat_with 1.28.0[−][src]

ⓘImportant traits for RepeatWith<F>

### Important traits for RepeatWith<F>

`impl<A, F: FnMut() -> A> Iterator for RepeatWith<F> type Item = A;`

    pub fn repeat_with<A, F: FnMut() -> A>(repeater: F) -> RepeatWith<F>

Creates a new iterator that repeats elements of type `A` endlessly by applying the provided closure, the repeater, `F: FnMut() -> A`.

The `repeat_with()` function calls the repeater over and over and over and over and over and 🔁.

Infinite iterators like `repeat_with()` are often used with adapters like `take`, in order to make them finite.

If the element type of the iterator you need implements `Clone`, and it is OK to keep the source element in memory, you should instead use the `repeat` function.

An iterator produced by `repeat_with()` is not a `DoubleEndedIterator`. If you need `repeat_with()` to return a `DoubleEndedIterator`, please open a GitHub issue explaining your use case.

# Examples

Basic usage:

    use std::iter;

    // let's assume we have some value of a type that is not `Clone`
    // or which don't want to have in memory just yet because it is expensive:
    #[derive(PartialEq, Debug)]
    struct Expensive;

    // a particular value forever:
    let mut things = iter::repeat_with(|| Expensive);

    assert_eq!(Some(Expensive), things.next());
    assert_eq!(Some(Expensive), things.next());
    assert_eq!(Some(Expensive), things.next());
    assert_eq!(Some(Expensive), things.next());
    assert_eq!(Some(Expensive), things.next());Run

Using mutation and going finite:

    use std::iter;

    // From the zeroth to the third power of two:
    let mut curr = 1;
    let mut pow2 = iter::repeat_with(|| { let tmp = curr; curr *= 2; tmp })
                        .take(4);

    assert_eq!(Some(1), pow2.next());
    assert_eq!(Some(2), pow2.next());
    assert_eq!(Some(4), pow2.next());
    assert_eq!(Some(8), pow2.next());

    // ... and now we're done
    assert_eq!(None, pow2.next());Run

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g. `str,u8` or `String,struct:Vec,test`)