edisp

Dispatch-on-collect for Rust enums.

This crate allows to dispatch enums yielded from an iterator, depending on their variants, with no runtime costs.

Note: This documentation describes what should be done, not the current state of the crate. Every feature documented here will be implemented prior first beta release.

Dispatching on std enums

This crate provides dispatching for enums defined in std. Values can be collected in any type that implements both Default and Extend traits. This dispatching consists in a trait generated for each enum, which can be called on every Iterator, like so:

use edisp::prelude::*;

// Use your regular iterator
let iter = vec![
    Ok(42),
    Ok(0),
    Err("User not found"),
    Err("System error"),
].into_iter();

// Call the correct method, and that's all!
let (some_successes, some_errors): (Vec<_>, Vec<_>) = iter.dispatch_result();

assert_eq!(some_successes, [42, 0]);
assert_eq!(some_errors, ["User not found", "System error"]);

Dispatching on other crate's enums

Dispatching code is generated with either derive macro or with declarative macro. The first method allows to quickly generate boilerplate without needing to write the enum name and variants twice. The second allows to get rid of the procedural macro dependencies, syn and quote, and reduces compilation time.

Values can then be collected in any type that implements both Default and Extend traits.

Using derive macro

This crate provides a custom derive macro allowing which automatically implements traits required for dispatching, as shown in the following code snippet:

use edisp::prelude::*;

#[derive(Dispatch)]
enum MyOwnEnum<T> {
    Character(char),
    Custom(T),
}

// Practical use-case:
// First, create an iterator of `MyOwnEnum<&'static str>`
let iter = vec![
    MyOwnEnum::Character('λ'),
    MyOwnEnum::Custom("horse"),
    MyOwnEnum::Custom("manatee"),
    MyOwnEnum::Character('!'),
].into_iter();

// Then call it
let (some_characters, some_strs): (Vec<_>, Vec<_>) = MyOwnEnum::dispatch(iter);

// And it does what you expect!
assert_eq!(
    some_characters,
    ['λ', '!'],
);

assert_eq!(
    some_strs,
    ["horse", "manatee"],
);

The custom derive feature can be disabled by disabling default-features in the cargo manifest.

Using declarative macro

This crate provides a macro entitled implement_dispatch. It allows to generate traits required for dispatching. Everything wraps up like this:

use edisp::prelude::*;

enum MyOwnEnum<T> {
    Character(char),
    Custom(T),
}

// Implements the required trait
implement_dispatch!(
    MyOwnEnum<T>,
    Character(char),
    Custom(T),
);

// Practical use-case:
// First, create an iterator of `MyOwnEnum<&'static str>`
let iter = vec![
    MyOwnEnum::Character('λ'),
    MyOwnEnum::Custom("horse"),
    MyOwnEnum::Custom("manatee"),
    MyOwnEnum::Character('!'),
].into_iter();

// Then call it
let (some_characters, some_strs): (Vec<_>, Vec<_>) = MyOwnEnum::dispatch(iter);

// And it does what you expect!
assert_eq!(
    some_characters,
    ['λ', '!'],
);

assert_eq!(
    some_strs,
    ["horse", "manatee"],
);

License: MIT OR Apache-2.0