derive_utils
A procedural macro helper for easily writing custom derives for enums.
Usage
Add this to your Cargo.toml
:
[dependencies]
derive_utils = "0.7"
The current version of derive_utils requires Rust 1.31 or later.
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 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 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,
Item,
trait ExactSizeIterator: Iterator {
fn len(&self) -> usize;
}
}
}
#[proc_macro_derive(FusedIterator)]
pub fn derive_fused_iterator(input: TokenStream) -> TokenStream {
quick_derive! {
input,
Item,
(std::iter::FusedIterator),
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>,
{
}
License
Licensed under either of
at your option.
Contribution
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.