✨ magic_static

Global singletons initialized at program start, an alternative to lazy initialization.

Usage

Simply add magic_static as a dependency in your Cargo.toml to get started:

[dependencies]
magic_static = "*"

bare-metal

If your target doesn't support atomics or threads, enable the bare-metal feature flag in your Cargo.toml:

[dependencies]
magic_static = { version = "*", features = ["bare-metal"] }

Example

#[macro_use]
extern crate magic_static;

mod foo {
    magic_statics! {
        pub(super) static ref MAGIC: usize = {
            println!("Magic!");
            42
        };

        pub(super) static ref BAR: std::sync::Mutex<()> = std::sync::Mutex::new(());
    }
}

// You can also modularize your magic statics in a group at the module level like so:
// See `main()` for how to initialize these magic statics.
mod baz {
    magic_statics_mod! {
        pub(super) static ref MAGIC: usize = {
            println!("Magic!");
            42
        };

        pub(super) static ref BAR: std::sync::Mutex<()> = std::sync::Mutex::new(());
    }
}

// You can also decorate statics to make them magic statics
#[magic_static]
static FOO_BAR: std::thread::JoinHandle<()> = {
    std::thread::spawn(move || {
        loop { println!("HELP I CANT STOP SPINNING"); }
    })
};

#[magic_static::main(
    FOO_BAR,

    foo::MAGIC,
    foo::BAR,

    mod baz // This will initialize all magic statics in the `baz` module
)]
fn main() {
    println!("Hello, world!");
}

Comparison to lazy_static

lazy_statics are initialized on first-use and are targetted towards multithreaded applications.

Every time a lazy_static is dereferenced, it must check whether it has been initialized yet. This is usually extremely cheap, and the resulting reference can be stored for use in hot loops (for example), but in some cases you may prefer no checks at all, i.e. a more lightweight solution.

magic_static only performs these checks in debug builds, making it a more ergonomic choice for single-threaded and performance-critical applications.

The downside of using magic_static is that you must manually initialize each magic_static in your main function or somewhere appropriate. See above for an example.