Crate derive_utils
source ·Expand description
A procedural macro helper for easily writing proc_macro_derive
like deriving trait to enum so long as all variants are implemented that trait.
Examples
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.
Crate Features
std
- Enabled by default.
- Generate code for
std
library. - Disable to generate code for
no_std
.
Rust Version
The current minimum required Rust version is 1.30.