#const #closures #nightly

nightly no-std const_closure

Helpers for creating const callable closures

7 releases

0.3.0 Nov 28, 2022
0.2.3 Nov 10, 2022
0.2.2 Sep 25, 2022
0.1.1 Sep 13, 2022

#120 in No standard library

40 downloads per month
Used in 2 crates (via const_sort_rs)


252 lines

Const Closure

Daily-Nightly Rust-Main-CI docs.rs crates.io rustc

This crate allows you to create types which represent closures in const contexts.

To do this simply create an instance of the provided closure helper: ConstClosure with the associated new function.

A closure helper instance gets the data to capture as a tuple of same ownership (Owned, Mut or ref) and the implementation function to execute.

The implementation function must be a const fn that gets the captured state (a tuple of: owned values for FnOnce, &mut for FnMut and & for Fn) and a tuple representing the arguments of the closure.

A closure helper instance returns the return value of the closure function on call.


#![feature(const_mut_refs)] // Only required for the FnMut example

use const_closure::ConstClosure;

// FnOnce:
const _: () = {
  const fn imp((state,): (i32,), (arg,): (i32,)) -> i32 {
    state + arg
  let cl = ConstClosure::new((5,), imp);
  assert!(7 == cl(2));

// FnMut:
const _: () = {
  const fn imp((state,): (&mut i32,), (arg,): (i32,)) -> i32 {
    *state += arg;
  let mut i = 5;
  let mut cl = ConstClosure::new((&mut i,), imp);

  assert!(7 == cl(2));
  assert!(8 == cl(1));

// Fn:
const _: () = {
  const fn imp((state,): (&i32,), (arg,): (i32,)) -> i32 {
    *state + arg
  let i = 5;
  let mut cl = ConstClosure::new((&i,), imp);
  assert!(7 == cl(2));
  assert!(8 == cl(3));
  assert!(6 == cl(1));

Note: The const_closure macro has been removed in favour of the new generic based approach.


raldone01 and onestacked are the primary authors and maintainers of this library.


This project is released under either:

at your choosing.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

No runtime deps