[−][src]Function nom::lib::std::convert::identity

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

🔬 This is a nightly-only experimental API. (convert_id)

An 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 among other interesting functions:

#![feature(convert_id)]
use std::convert::identity;

fn manipulation(x: u32) -> u32 {
    // Let's assume that this function does something interesting.
    x + 1
}

let _arr = &[identity, manipulation];

Using identity to get a function that changes nothing in a conditional:

#![feature(convert_id)]
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>:

#![feature(convert_id)]
use std::convert::identity;

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