daywalker

Write nightly-conditional code once. Run on both nightly and stable Rust.

#![cfg_attr(feature = "nightly", feature(const_trait_impl))]

daywalker::roam! {
    pub ++[const] trait Name {
        fn name(&self) -> &'static str;
    }

    impl ++[const] Name for () {
        fn name(&self) -> &'static str {
            ++["nightly"] --["stable"]
        }
    }
}

fn main() {
    println!("Hello, {}!", ().name());
}

Perfect for library authors - write once, let users choose between nightly features or stable compatibility.

How it works

1. Use the function-like proc-macro: roam! { ... }.
2. Inside the proc-macro, use the conditional operators ("bitemarks"):

• ++[...]: Emit code only when nightly feature is enabled
• --[...]: Emit code only when nightly feature is disabled

Features

• Zero-cost - Simple conditional inclusion, no runtime overhead
• Forward compatible - Easy migration when nightly features stabilize
• Lightweight - Single proc-macro, no dependencies
• Flexible - Works with any nightly-specific syntax or tokens
• Granular control - Conditionally include any code block or token

For Library Authors

Write nightly-optional code that work for everyone! First, expose the choice to your library users:

# Cargo.toml
[package]
name = "cool-lib"
version = "1.0.0"

[dependencies]
daywalker = "1.0"

[features]
nightly = ["daywalker/nightly"]

Then, define and implement conditional code using the nightly syntax with prefix operators:

// src/lib.rs
#![cfg_attr(feature = "nightly", feature(const_trait_impl))]

daywalker::roam! {
    pub ++[const] trait Compute {
        fn compute(&self) -> u32;
    }

    impl ++[const] Compute for u32 {
        fn compute(&self) -> u32 { *self * 2 }
    }
}

For Library Users

Stable

If you want to run on stable rust, use the library like normal. First, add the dependency:

# Cargo.toml
[dependencies]
cool-lib = "1.0"

Then use the dependency:

// src/main.rs
use cool_lib::Compute;
let value: u32 = 42u32.compute(); // ✅ Runtime

That's it!

Nightly

On the other hand, if you want that sweet nightly functionality and are willing to accept the requirement to compile only on nightly, then just use the nightly feature:

# Cargo.toml
[dependencies]
cool-lib = { version = "1.0", features = ["nightly"] }

Look, you get nightly features!

// src/main.rs
#![feature(const_trait_impl)]
use cool_lib::Compute;
const VALUE: u32 = 42u32.compute(); // ✅ Compile-time