cfg-if

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A if/elif-like macro for Rust #[cfg] statements

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About

A if/elif-like macro for Rust #[cfg] statements

cfg-if

[!WARNING] This crate has been "replaced" by the cfg_select! macro, which is stable since Rust 1.95.0 with a slightly different syntax. Barring breakages and security fixes, this crate will no longer be updated.

Documentation

A macro to ergonomically define an item depending on a large number of #[cfg] parameters. Structured like an if-else chain, the first matching branch is the item that gets emitted.

toml

[dependencies]
cfg-if = "1.0"

Example

rust

cfg_if::cfg_if! {
    if #[cfg(unix)] {
        fn foo() { /* unix specific functionality */ }
    } else if #[cfg(target_pointer_width = "32")] {
        fn foo() { /* non-unix, 32-bit functionality */ }
    } else {
        fn foo() { /* fallback implementation */ }
    }
}

fn main() {
    foo();
}

The cfg_if! block above is expanded to:

rust

#[cfg(unix)]
fn foo() { /* unix specific functionality */ }
#[cfg(all(target_pointer_width = "32", not(unix)))]
fn foo() { /* non-unix, 32-bit functionality */ }
#[cfg(not(any(unix, target_pointer_width = "32")))]
fn foo() { /* fallback implementation */ }

License

This project is licensed under either of

Apache License, Version 2.0, (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
MIT license (LICENSE-MIT or https://opensource.org/licenses/MIT)

at your option.

Contribution

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