https://github.com/taiki-e/const_fn

A lightweight attribute for easy generation of const functions with conditional compilations.
https://github.com/taiki-e/const_fn

no-std proc-macro rust

Last synced: 4 days ago
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A lightweight attribute for easy generation of const functions with conditional compilations.

• Host: GitHub
• URL: https://github.com/taiki-e/const_fn
• Owner: taiki-e
• License: apache-2.0
• Created: 2018-12-25T19:58:23.000Z (almost 6 years ago)
• Default Branch: main
• Last Pushed: 2024-10-20T18:36:12.000Z (about 1 month ago)
• Last Synced: 2024-10-29T12:58:13.315Z (22 days ago)
• Topics: no-std, proc-macro, rust
• Language: Shell
• Homepage: https://docs.rs/const_fn
• Size: 270 KB
• Stars: 26
• Watchers: 5
• Forks: 2
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE-APACHE

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README

        
# \#\[const_fn\]

[![crates.io](https://img.shields.io/crates/v/const_fn?style=flat-square&logo=rust)](https://crates.io/crates/const_fn)

[![docs.rs](https://img.shields.io/badge/docs.rs-const__fn-blue?style=flat-square&logo=docs.rs)](https://docs.rs/const_fn)

[![license](https://img.shields.io/badge/license-Apache--2.0_OR_MIT-blue?style=flat-square)](#license)

[![msrv](https://img.shields.io/badge/msrv-1.31-blue?style=flat-square&logo=rust)](https://www.rust-lang.org)

[![github actions](https://img.shields.io/github/actions/workflow/status/taiki-e/const_fn/ci.yml?branch=main&style=flat-square&logo=github)](https://github.com/taiki-e/const_fn/actions)

A lightweight attribute for easy generation of const functions with conditional

compilations.

## Usage

Add this to your `Cargo.toml`:

```toml

[dependencies]

const_fn = "0.4"

```

## Examples

```rust

use const_fn::const_fn;

// function is `const` on specified version and later compiler (including beta, nightly, and dev build)

#[const_fn("1.36")]

pub const fn version() {

    /* ... */

}

// function is `const` on nightly compiler (including dev build)

#[const_fn(nightly)]

pub const fn nightly() {

    /* ... */

}

// function is `const` if `cfg(...)` is true

#[const_fn(cfg(...))]

pub const fn cfg() {

    /* ... */

}

// function is `const` if `cfg(feature = "...")` is true

#[const_fn(feature = "...")]

pub const fn feature() {

    /* ... */

}

```

### Use this crate as an optional dependency

If no arguments are passed, `const_fn` will always make the function `const`.

Therefore, you can use `const_fn` as an optional dependency by combination with `cfg_attr`.

```rust

// function is `const` if `cfg(feature = "...")` is true

#[cfg_attr(feature = "...", const_fn::const_fn)]

pub fn optional() {

    /* ... */

}

```

## Alternatives

This crate is proc-macro, but is very lightweight, and has no dependencies.

You can manually define declarative macros with similar functionality (see

[`if_rust_version`](https://github.com/ogoffart/if_rust_version#examples)),

or [you can define the same function twice with different cfg](https://github.com/crossbeam-rs/crossbeam/blob/0b6ea5f69fde8768c1cfac0d3601e0b4325d7997/crossbeam-epoch/src/atomic.rs#L340-L372).

(Note: the former approach requires more macros to be defined depending on the

number of version requirements, the latter approach requires more functions to

be maintained manually)

## License

Licensed under either of [Apache License, Version 2.0](LICENSE-APACHE) or

[MIT license](LICENSE-MIT) at your option.

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.