derive_utils
A procedural macro helper for easily writing derives macros for enums.
Usage
Add this to your Cargo.toml
:
[dependencies]
derive_utils = "0.14"
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.
use derive_utils::quick_derive;
use proc_macro::TokenStream;
#[proc_macro_derive(Iterator)]
pub fn derive_iterator(input: TokenStream) -> TokenStream {
quick_derive! {
input,
std::iter::Iterator,
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,
std::iter::ExactSizeIterator,
<Item>,
trait ExactSizeIterator: Iterator {
fn len(&self) -> usize;
}
}
}
Generated code
When deriving for enum like the following:
#[derive(Iterator, ExactSizeIterator, Future)]
enum Enum<A, B> {
A(A),
B(B),
}
Code like this will be generated:
enum Enum<A, B> {
A(A),
B(B),
}
impl<A, B> std::iter::Iterator for Enum<A, B>
where
A: std::iter::Iterator,
B: std::iter::Iterator<Item = <A as std::iter::Iterator>::Item>,
{
type Item = <A as std::iter::Iterator>::Item;
fn next(&mut self) -> Option<Self::Item> {
match self {
Enum::A(x) => x.next(),
Enum::B(x) => x.next(),
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
match self {
Enum::A(x) => x.size_hint(),
Enum::B(x) => x.size_hint(),
}
}
}
impl<A, B> std::iter::ExactSizeIterator for Enum<A, B>
where
A: std::iter::ExactSizeIterator,
B: std::iter::ExactSizeIterator<Item = <A as Iterator>::Item>,
{
fn len(&self) -> usize {
match self {
Enum::A(x) => x.len(),
Enum::B(x) => x.len(),
}
}
}
Related Projects
- auto_enums: A library for to allow multiple return types by automatically generated enum.
- io-enum: #[derive(Read, Write, Seek, BufRead)] for enums.
- iter-enum: #[derive(Iterator, DoubleEndedIterator, ExactSizeIterator, FusedIterator, Extend)] for enums.
License
Licensed under either of Apache License, Version 2.0 or
MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.