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lib.rs
This crate provides helper types for matching against enum variants, and extracting bindings to each of the fields in the deriving Struct or Enum in a generic way. If you are writing a `#[derive]` which needs to perform some operation on every field, then you have come to the right place! # Example: `WalkFields` ### Trait Implementation ``` pub trait WalkFields: std::any::Any { fn walk_fields(&self, walk: &mut FnMut(&WalkFields)); } impl WalkFields for i32 { fn walk_fields(&self, _walk: &mut FnMut(&WalkFields)) {} } ``` ### Custom Derive ``` # use quote::quote; fn walkfields_derive(s: synstructure::Structure) -> proc_macro2::TokenStream { let body = s.each(|bi| quote!{ walk(#bi) }); s.gen_impl(quote! { extern crate synstructure_test_traits; gen impl synstructure_test_traits::WalkFields for @Self { fn walk_fields(&self, walk: &mut FnMut(&synstructure_test_traits::WalkFields)) { match *self { #body } } } }) } # const _IGNORE: &'static str = stringify!( synstructure::decl_derive!([WalkFields] => walkfields_derive); # ); /* * Test Case */ fn main() { synstructure::test_derive! { walkfields_derive { enum A<T> { B(i32, T), C(i32), } } expands to { const _: () = { extern crate synstructure_test_traits; impl<T> synstructure_test_traits::WalkFields for A<T> where T: synstructure_test_traits::WalkFields { fn walk_fields(&self, walk: &mut FnMut(&synstructure_test_traits::WalkFields)) { match *self { A::B(ref __binding_0, ref __binding_1,) => { { walk(__binding_0) } { walk(__binding_1) } } A::C(ref __binding_0,) => { { walk(__binding_0) } } } } } }; } } } ``` # Example: `Interest` ### Trait Implementation ``` pub trait Interest { fn interesting(&self) -> bool; } impl Interest for i32 { fn interesting(&self) -> bool { *self > 0 } } ``` ### Custom Derive ``` # use quote::quote; fn interest_derive(mut s: synstructure::Structure) -> proc_macro2::TokenStream { let body = s.fold(false, |acc, bi| quote!{ #acc || synstructure_test_traits::Interest::interesting(#bi) }); s.gen_impl(quote! { extern crate synstructure_test_traits; gen impl synstructure_test_traits::Interest for @Self { fn interesting(&self) -> bool { match *self { #body } } } }) } # const _IGNORE: &'static str = stringify!( synstructure::decl_derive!([Interest] => interest_derive); # ); /* * Test Case */ fn main() { synstructure::test_derive!{ interest_derive { enum A<T> { B(i32, T), C(i32), } } expands to { const _: () = { extern crate synstructure_test_traits; impl<T> synstructure_test_traits::Interest for A<T> where T: synstructure_test_traits::Interest { fn interesting(&self) -> bool { match *self { A::B(ref __binding_0, ref __binding_1,) => { false || synstructure_test_traits::Interest::interesting(__binding_0) || synstructure_test_traits::Interest::interesting(__binding_1) } A::C(ref __binding_0,) => { false || synstructure_test_traits::Interest::interesting(__binding_0) } } } } }; } } } ``` For more example usage, consider investigating the `abomonation_derive` crate, which makes use of this crate, and is fairly simple.
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macros.rs
This module provides two utility macros for testing custom derives. They can be used together to eliminate some of the boilerplate required in order to declare and test custom derive implementations.
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