#[const_fn]

An attribute for easy generation of a const function with conditional compilations.

Usage

Add this to your Cargo.toml:

[dependencies]
const_fn = "0.3"

The current const_fn requires Rust 1.31 or later.

Examples

When using like the following functions to control unstable features:

[features]
const_unstable = []

It can be written as follows:

#![cfg_attr(feature = "const_unstable", feature(const_fn))]
use const_fn::const_fn;

pub struct Foo<T> {
    x:T,
}

impl<T: Iterator> Foo<T> {
    /// Constructs a new `Foo`.
    #[const_fn(feature = "const_unstable")]
    pub const fn new(x: T) -> Self {
        Self { x }
    }
}

Code like this will be generated:

#![cfg_attr(feature = "const_unstable", feature(const_fn))]

pub struct Foo<T> {
    x:T,
}

impl<T: Iterator> Foo<T> {
    /// Constructs a new `Foo`.
    #[cfg(feature = "const_unstable")]
    pub const fn new(x: T) -> Self {
        Self { x }
    }

    /// Constructs a new `Foo`.
    #[cfg(not(feature = "const_unstable"))]
    pub fn new(x: T) -> Self {
        Self { x }
    }
}

See test_suite for more examples.

License

Licensed under either of

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

at your option.

Contribution

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.