Crate derive_utils

A procedural macro helper for easily writing custom derives for enums.

Examples

quick_derive! macro make easy to write proc_macro_derive like deriving trait to enum so long as all variants are implemented that trait.

extern crate derive_utils;
extern crate proc_macro;

use derive_utils::quick_derive;
use proc_macro::TokenStream;

#[proc_macro_derive(Iterator)]
pub fn derive_iterator(input: TokenStream) -> TokenStream {
    quick_derive! {
        input,
        // trait
        trait Iterator {
            type Item;
            fn next(&mut self) -> Option<Self::Item>;
            fn size_hint(&self) -> (usize, Option<usize>);
        }
    }
}

#[proc_macro_derive(ExactSizeIterator)]
pub fn derive_exact_size_iterator(input: TokenStream) -> TokenStream {
    quick_derive! {
        input,
        // super trait's associated types
        Item,
        // trait
        trait ExactSizeIterator: Iterator {
            fn len(&self) -> usize;
        }
    }
}

#[proc_macro_derive(FusedIterator)]
pub fn derive_fused_iterator(input: TokenStream) -> TokenStream {
    quick_derive! {
        input,
        // super trait's associated types
        Item,
        // path
        (std::iter::FusedIterator),
        // trait
        trait FusedIterator: Iterator {},
    }
}

Generated code

When deriving for enum like the following:

#[derive(Iterator, ExactSizeIterator, FusedIterator)]
enum Iter<A, B> {
    A(A),
    B(B),
}

Code like this will be generated:

enum Iter<A, B> {
    A(A),
    B(B),
}

impl<A, B> Iterator for Iter<A, B>
where
    A: Iterator,
    B: Iterator<Item = <A as Iterator>::Item>,
{
    type Item = <A as Iterator>::Item;
    fn next(&mut self) -> Option<Self::Item> {
        match self {
            Iter::A(x) => x.next(),
            Iter::B(x) => x.next(),
        }
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        match self {
            Iter::A(x) => x.size_hint(),
            Iter::B(x) => x.size_hint(),
        }
    }
}

impl<A, B> ExactSizeIterator for Iter<A, B>
where
    A: ExactSizeIterator,
    B: ExactSizeIterator<Item = <A as Iterator>::Item>,
{
    fn len(&self) -> usize {
        match self {
            Iter::A(x) => x.len(),
            Iter::B(x) => x.len(),
        }
    }
}

impl<A, B> std::iter::FusedIterator for Iter<A, B>
where
    A: std::iter::FusedIterator,
    B: std::iter::FusedIterator<Item = <A as Iterator>::Item>,
{
}

See auto_enums crate for more examples.

Macros

derive_trait
quick_derive	A macro for to make easy to write proc_macro_derive like deriving trait to enum so long as all variants are implemented that trait.

Structs

EnumData	A structure to make trait implementation to enums more efficient.
EnumElements	The elements that compose enums.
EnumImpl	A builder for implementing traits for enums.

Enums

Error

Traits

MaybeEnum

A type that might be enums.

Functions

compile_err

Type Definitions

Result