identity in core::convert - Rust
Description: The identity function.

## identity

# Function identity

1.33.0 (const: 1.33.0) · Source

    pub const fn identity<T>(x: T) -> T

Expand description

The identity function.

Two things are important to note about this function:

- It is not always equivalent to a closure like `|x| x`, since the closure may coerce `x` into a different type.

- It moves the input `x` passed to the function.

While it might seem strange to have a function that just returns back the input, there are some interesting uses.

## §Examples

Using `identity` to do nothing in a sequence of other, interesting, functions:

    use std::convert::identity;

    fn manipulation(x: u32) -> u32 {
        // Let's pretend that adding one is an interesting function.
        x + 1
    }

    let _arr = &[identity, manipulation];

Using `identity` as a “do nothing” base case in a conditional:

    use std::convert::identity;

    let do_stuff = if condition { manipulation } else { identity };

    // Do more interesting stuff...

    let _results = do_stuff(42);

Using `identity` to keep the `Some` variants of an iterator of `Option<T>`:

    use std::convert::identity;

    let iter = [Some(1), None, Some(3)].into_iter();
    let filtered = iter.filter_map(identity).collect::<Vec<_>>();
    assert_eq!(vec![1, 3], filtered);