#lifetime #lifetimes #reference #temp #type

no-std dyn-context

Simple mechanism for lifetimes erasing

46 releases (18 breaking)

0.18.0 Jun 4, 2022
0.16.1 May 17, 2022
0.10.8 Sep 24, 2021
0.7.0 Jul 26, 2021
0.3.2 Sep 21, 2020

#446 in Rust patterns

41 downloads per month
Used in dep-obj


341 lines

maintenance: experimental


This crate provides simple mechanism for lifetimes erasing.

In Rust, lifetimes are intrusive, and sometimes it can lead to an inadequately complex code. Moreover, in some cases it can lead to an impossible code, means code so complex, so it can not make to compile, even it is logically meaningful. (Such situations could occur because Rust does not support existential types with infinite parameters list.)

The crate provides a way to "compress" several lifetimed references into a one reference to a 'static type. This mechanism guarantees type-safety.

This mechanics allows building complex systems with callbacks:

mod call_back {
    pub struct CallBack<State: ?Sized> {
        callback: Option<fn(state: &mut State)>

    impl<State: ?Sized> CallBack<State> {
        pub fn new() -> Self { CallBack { callback: None } }

        pub fn set_callback(&mut self, callback: fn(state: &mut State)) {

        pub fn call_back(&self, state: &mut State) {
            self.callback.map(|callback| callback(state));

use call_back::CallBack;
use dyn_context::free_lifetimes;

free_lifetimes! {
    struct PrintState {
        value: 'value ref str

fn main() {
    let mut call_back = CallBack::new();
    call_back.set_callback(|state: &mut PrintState| {
        println!("{}", state.value());
    PrintStateBuilder {
        value: "Hello, world!"