Crate synstructure [−] [src]
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
#[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.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 } } } }) } 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_synstructure_test_traits_WalkFields_FOR_A: () = { 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
#[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 || 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 } } } }) } 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_synstructure_test_traits_Interest_FOR_A: () = { 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.
Macros
decl_derive |
The |
quote |
The whole point. |
quote_spanned |
Same as |
test_derive |
Run a test on a custom derive. This macro expands both the original struct and the expansion to ensure that they compile correctly, and confirms that feeding the original struct into the named derive will produce the written output. |
Structs
BindingInfo |
Information about a specific binding. This contains both an |
Structure |
A wrapper around a |
VariantAst |
This type is similar to |
VariantInfo |
A wrapper around a |
Enums
BindStyle |
The type of binding to use when generating a pattern. |
Functions
unpretty_print |
Dumps an unpretty version of a tokenstream. Takes any type which implements
|