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 condition = true;
#
# fn manipulation(x: u32) -> u32 { x + 1 }
#
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);