[−][src]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 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 {}, } } #[proc_macro_derive(Future)] pub fn derive_future(input: TokenStream) -> TokenStream { quick_derive! { input, // path (std::future::Future), // trait trait Future { type Output; fn poll(self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> std::task::Poll<Self::Output>; } } }
Generated code
When deriving for enum like the following:
#[derive(Iterator, ExactSizeIterator, FusedIterator, 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> Iterator for Enum<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 { 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> ExactSizeIterator for Enum<A, B> where A: ExactSizeIterator, B: ExactSizeIterator<Item = <A as Iterator>::Item>, { fn len(&self) -> usize { match self { Enum::A(x) => x.len(), Enum::B(x) => x.len(), } } } impl<A, B> std::iter::FusedIterator for Enum<A, B> where A: std::iter::FusedIterator, B: std::iter::FusedIterator<Item = <A as Iterator>::Item>, { } impl<A, B> std::future::Future for Enum<A, B> where A: std::future::Future, B: std::future::Future<Output = <A as std::future::Future>::Output>, { type Output = <A as std::future::Future>::Output; fn poll( self: std::pin::Pin<&mut Self>, cx: &mut std::task::Context<'_>, ) -> std::task::Poll<Self::Output> { unsafe { match self.get_unchecked_mut() { Enum::A(x) => std::pin::Pin::new_unchecked(x).poll(cx), Enum::B(x) => std::pin::Pin::new_unchecked(x).poll(cx), } } } }
See auto_enums crate for more examples.
Macros
derive_trait | |
quick_derive | A macro for to make easy to write |
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. |
Traits
MaybeEnum | A type that might be enums. |