https://github.com/matklad/typed_index_derive

https://github.com/matklad/typed_index_derive

Last synced: about 1 month ago
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• Host: GitHub
• URL: https://github.com/matklad/typed_index_derive
• Owner: matklad
• License: apache-2.0
• Created: 2018-06-03T20:53:28.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2018-06-19T13:52:59.000Z (over 6 years ago)
• Last Synced: 2024-09-14T12:52:12.311Z (2 months ago)
• Language: Rust
• Size: 9.77 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE-APACHE

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README

        
# typed_index_derive

[![Build Status](https://travis-ci.org/matklad/typed_index_derive.svg?branch=master)](https://travis-ci.org/matklad/typed_index_derive)

[![Crates.io](https://img.shields.io/crates/v/typed_index_derive.svg)](https://crates.io/crates/typed_index_derive)

[![API reference](https://docs.rs/typed_index_derive/badge.svg)](https://docs.rs/typed_index_derive/)

Custom derive to easily create newtype index types.

A frequent pattern in Rust is to store objects in a vector and use integer indexes

as handlers to them. While using `usize` works, it could become confusing if there

are several flavors of indexes. To make the meaning of each index clear the newtype

wrappers like `FooIdx(usize)` are useful, but require a fair amount of boilerplate.

This crate derives the boilerplate for you:

```rust

#[macro_use]

extern crate typed_index_derive;

struct Spam(String);

#[derive(

    // Usual derives for plain old data

    Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Hash,

    // this crate

    TypedIndex

)]

#[typed_index(Spam)] // index into `&[Spam]`

struct SpamIdx(usize); // could be `u32` instead of `usize`

fn main() {

    let spams = vec![Spam("foo".into()), Spam("bar".into()), Spam("baz".into())];

    // Conversions between `usize` and `SpamIdx`

    let idx: SpamIdx = 1.into();

    assert_eq!(usize::from(idx), 1);

    // We can index `Vec` with SpamIdx

    assert_eq!(&spams[idx].0, "bar");

    // However, we can't index `Vec`

    // vec![1, 2, 3][idx]

    // error: slice indices are of type `usize` or ranges of `usize`

    // You can add/subtract `usize` from an index

    assert_eq!(&spams[idx - 1].0, "foo");

    // The difference between two indices is `usize`

    assert_eq!(idx - idx, 0usize);

}

```