Rust hot lib-reloader

A simple crate around libloading that can be used to watch Rust libraries (dylibs) and will reload them again when they have changed. Useful for changing code and seeing the effects without having to restart the app.

Note: This is meant to be used for development! Don't use it in production!

Usage

Assuming you use a workspace with the following layout:

• Cargo.toml
• crates/lib/Cargo.toml
• crates/lib/src/lib.rs
• crates/bin/Cargo.toml
• crates/bin/src/main.rs

lib

The library should expose functions and state. It should have specify dylib as crate type. The crates/lib/Cargo.toml:

```toml [package] name = "lib" version = "0.1.0" edition = "2021"

[lib] crate-type = ["rlib", "dylib"] ```

And crates/lib/lib.rs

```rust

[no_mangle]

pub extern "C" fn do_stuff() { println!("doing stuff"); } ```

bin

In the binary, use the lib and lot hot-lib-reloader. The bin/Cargo.toml:

```toml [package] name = "bin" version = "0.1.0" edition = "2021"

[dependencies] lib = { path = "../lib" } hot-lib-reloader = { path = "../../../hot-lib-reloader", optional = true }

[features] default = [] reload = ["dep:hot-lib-reloader"] ```

In the main function check if the lib has changed and call the exported function:

```rust

[cfg(feature = "reload")]

use hotlibreloader::LibReloader;

fn main() { #[cfg(feature = "reload")] let mut lib_loader = LibReloader::new("target/debug", "liblib").expect("initial load the lib");

loop {
    #[cfg(feature = "reload")]
    lib_loader.update().expect("lib update"); # will reload lib on change

    #[cfg(feature = "reload")]
    unsafe {
        lib_loader
            .get_symbol::<fn()>(b"do_stuff\0")
            .expect("Load do_stuff()")();
    };
    #[cfg(not(feature = "reload"))]
    lib::do_stuff();

    std::thread::sleep(std::time::Duration::from_secs(1));
}

} ```

Running it

To start compilation of the library:

shell cargo watch -w crates/lib -x build

And in addition to that start compilation of the binary with reload enabled:

shell cargo watch -w crates/bin -x 'run --features reload'

A change that you now make to crates/lib/lib.rs will have an immediate effect on the app.