commit | 909fe9a38cd5117d65abd2c17df4eadd646a2e34 | [log] [tgz] |
---|---|---|
author | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Fri Jul 07 04:52:55 2023 +0000 |
committer | Android Build Coastguard Worker <android-build-coastguard-worker@google.com> | Fri Jul 07 04:52:55 2023 +0000 |
tree | 59208246e5b7735408dba2aeccc91c760520074b | |
parent | 3ecd884aa59f54921538441b71d9f55b48e9acd9 [diff] | |
parent | 13de129ed5af2d1652c6a4d3d2e7d5e37e84d394 [diff] |
Snap for 10453563 from 13de129ed5af2d1652c6a4d3d2e7d5e37e84d394 to mainline-documentsui-release Change-Id: Ic74693ccaaf7aefc8b807e7c10f417e5aa436a4c
NOTE: What follows is an exerpt from the module level documentation. For full details read the docs on docs.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!
WalkFields
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)) {} }
#[macro_use] extern crate synstructure; #[macro_use] extern crate quote; extern crate proc_macro2; fn walkfields_derive(s: synstructure::Structure) -> proc_macro2::TokenStream { let body = s.each(|bi| quote!{ walk(#bi) }); s.bound_impl(quote!(example_traits::WalkFields), quote!{ fn walk_fields(&self, walk: &mut FnMut(&example_traits::WalkFields)) { match *self { #body } } }) } decl_derive!([WalkFields] => walkfields_derive); /* * Test Case */ fn main() { test_derive! { walkfields_derive { enum A<T> { B(i32, T), C(i32), } } expands to { #[allow(non_upper_case_globals)] const _DERIVE_example_traits_WalkFields_FOR_A: () = { extern crate example_traits; impl<T> example_traits::WalkFields for A<T> where T: example_traits::WalkFields { fn walk_fields(&self, walk: &mut FnMut(&example_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) } } } } } }; } } }
Interest
pub trait Interest { fn interesting(&self) -> bool; } impl Interest for i32 { fn interesting(&self) -> bool { *self > 0 } }
#[macro_use] extern crate synstructure; #[macro_use] extern crate quote; extern crate proc_macro2; fn interest_derive(mut s: synstructure::Structure) -> proc_macro2::TokenStream { let body = s.fold(false, |acc, bi| quote!{ #acc || example_traits::Interest::interesting(#bi) }); s.bound_impl(quote!(example_traits::Interest), quote!{ fn interesting(&self) -> bool { match *self { #body } } }) } decl_derive!([Interest] => interest_derive); /* * Test Case */ fn main() { test_derive!{ interest_derive { enum A<T> { B(i32, T), C(i32), } } expands to { #[allow(non_upper_case_globals)] const _DERIVE_example_traits_Interest_FOR_A: () = { extern crate example_traits; impl<T> example_traits::Interest for A<T> where T: example_traits::Interest { fn interesting(&self) -> bool { match *self { A::B(ref __binding_0, ref __binding_1,) => { false || example_traits::Interest::interesting(__binding_0) || example_traits::Interest::interesting(__binding_1) } A::C(ref __binding_0,) => { false || example_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.