synstructure

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!

Example: WalkFields

Trait Implementation

rust 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

```rust

[macro_use]

extern crate synstructure;

[macro_use]

extern crate quote;

fn walkfields_derive(s: synstructure::Structure) -> quote::Tokens { 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 }
    }
})

} declderive!([WalkFields] => walkfieldsderive);

/* * Test Case */ fn main() { testderive! { walkfieldsderive { enum A { B(i32, T), C(i32), } } expands to { #[allow(nonuppercaseglobals)] const _DERIVEexampletraitsWalkFieldsFORA: () = { extern crate exampletraits; impl exampletraits::WalkFields for A where T: exampletraits::WalkFields { fn walkfields(&self, walk: &mut FnMut(&exampletraits::WalkFields)) { match *self { A::B(ref binding0, ref _binding1,) => { { walk(binding0) } { walk(binding1) } } A::C(ref _binding0,) => { { walk(binding_0) } } } } } }; } } } ```

Example: Interest

Trait Implementation

rust pub trait Interest { fn interesting(&self) -> bool; } impl Interest for i32 { fn interesting(&self) -> bool { *self > 0 } }

Custom Derive

```rust

[macro_use]

extern crate synstructure;

[macro_use]

extern crate quote;

fn interestderive(mut s: synstructure::Structure) -> quote::Tokens { let body = s.fold(false, |acc, bi| quote!{ #acc || exampletraits::Interest::interesting(#bi) });

s.bound_impl(quote!(example_traits::Interest), quote!{
    fn interesting(&self) -> bool {
        match *self {
            #body
        }
    }
})

} declderive!([Interest] => interestderive);

/* * Test Case */ fn main() { testderive!{ interestderive { enum A { B(i32, T), C(i32), } } expands to { #[allow(nonuppercaseglobals)] const _DERIVEexampletraitsInterestFORA: () = { extern crate exampletraits; impl exampletraits::Interest for A where T: exampletraits::Interest { fn interesting(&self) -> bool { match *self { A::B(ref binding0, ref _binding1,) => { false || exampletraits::Interest::interesting(binding0) || exampletraits::Interest::interesting(binding1) } A::C(ref _binding0,) => { false || exampletraits::Interest::interesting(binding0) } } } } }; } } } ```

For more example usage, consider investigating the abomonation_derive crate, which makes use of this crate, and is fairly simple.