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 methods 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 Usage

extern crate syn;
extern crate synstructure;
#[macro_use]
extern crate quote;
use synstructure::{each_field, BindStyle};

type TokenStream = String; // XXX: Dummy to not depend on rustc_macro

fn sum_fields_derive(input: TokenStream) -> TokenStream {
    let source = input.to_string();
    let ast = syn::parse_macro_input(&source).unwrap();

    let match_body = each_field(&ast, &BindStyle::Ref.into(), |bi| quote! {
        sum += #bi as i64;
    });

    let name = &ast.ident;
    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
    let result = quote! {
        impl #impl_generics ::sum_fields::SumFields for #name #ty_generics #where_clause {
            fn sum_fields(&self) -> i64 {
                let mut sum = 0i64;
                match *self { #match_body }
                sum
            }
        }
    };

    result.to_string().parse().unwrap()
}

fn main() {}

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