https://github.com/ohsayan/constant

Constant, compile-time evaluation tools for Rust
https://github.com/ohsayan/constant

const-evaluation crates-io macro rust rust-lang rust-library

Last synced: 4 months ago
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Constant, compile-time evaluation tools for Rust

• Host: GitHub
• URL: https://github.com/ohsayan/constant
• Owner: ohsayan
• License: apache-2.0
• Created: 2021-09-30T06:53:15.000Z (about 4 years ago)
• Default Branch: next
• Last Pushed: 2021-10-01T05:25:59.000Z (about 4 years ago)
• Last Synced: 2025-06-18T18:04:51.693Z (4 months ago)
• Topics: const-evaluation, crates-io, macro, rust, rust-lang, rust-library
• Language: Rust
• Homepage: https://docs.rs/constant
• Size: 29.3 KB
• Stars: 2
• Watchers: 2
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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README

          
# `constant`: Constant, compile-time evaluation tools for Rust 🦀

![Rust Stable](https://img.shields.io/badge/rust-stable-50C878?style=for-the-badge) ![GitHub Workflow Status](https://img.shields.io/github/workflow/status/ohsayan/constant/Test?style=for-the-badge) [![Crates.io](https://img.shields.io/crates/v/constant?style=for-the-badge)](https://crates.io/crates/constant) [![docs.rs](https://img.shields.io/docsrs/constant?style=for-the-badge)](https://docs.rs/constant) [![GitHub](https://img.shields.io/github/license/ohsayan/constant?style=for-the-badge)](./LICENSE)

The `constant` crate aims to provide tools for safely _working around_ the limits imposed by constant evaluation in Rust.

## Features

- Create [constant default implementations](#constant-default-implementations)

- Created [nested constant default implementations](#nested-constant-default-implementations)

- Full support for generics, lifetimes and generics in `Constdef` impls

- Almost all types provided by the `std` are supported by this crate. If you need any other external type, [just open an issue and ask!](https://github.com/ohsayan/constant/issues/new)

- More coming soon!

## Constant default implementations

```rust

#[derive(constant::Constdef)]

pub struct SpookyFriend {

    name: String,

    email: String,

    friend_names: Vec,

    userid: u64,

}

const SPOOKY: SpookyFriend = SpookyFriend::default();

#[test]

fn test_struct_with_heap_fields() {

    // spooky name; it's empty!

    assert_eq!(SPOOKY.name, "");

    // spooky email; it's empty!

    assert_eq!(SPOOKY.email, "");

    // spooky friend has no friends!

    assert_eq!(SPOOKY.friend_names, Vec::::new());

    // spooky userid; it's 0!

    assert_eq!(SPOOKY.userid, 0);

}

```

## Nested constant default implementations

```rust

use constant::Constdef;

#[derive(Constdef)]

pub struct SystemLoad {

    disk: DiskLoad,

    net: NetLoad,

}

#[derive(Constdef)]

pub struct DiskLoad {

    disk_count: usize,

    media_list: Vec,

}

#[derive(Constdef)]

pub struct NetLoad {

    interface_list: Vec,

    portload: [usize; 65536],

}

static mut SYSLOAD: SystemLoad = SystemLoad::default();

#[test]

fn test_system_load_nested_struct() {

    unsafe {

        // check the number of disks

        assert_eq!(SYSLOAD.disk.disk_count, 0);

        // increment the number of disks

        SYSLOAD.disk.disk_count += 1;

        assert_eq!(SYSLOAD.disk.disk_count, 1);

        // check port 80 load

        assert_eq!(SYSLOAD.net.portload[80], 0);

        // increment the load

        SYSLOAD.net.portload[80] += 1;

        assert_eq!(SYSLOAD.net.portload[80], 1);

        // now let's add a disk

        SYSLOAD.disk.media_list.push("/dev/sda1".to_string());

        // now let's add a network interface

        SYSLOAD.net.interface_list.push("eth01".to_string());

    }

}

```

## License

This library is distributed under the [Apache-2.0 License](./LICENSE).