gistfile1.rs

extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;

use proc_macro::TokenStream;

#[proc_macro_derive(QueryParams)]
pub fn derive_query_params(input: TokenStream) -> TokenStream {
  let ast: syn::DeriveInput = syn::parse(input).expect("Could not derive QueryParams struct");
  let name = ast.ident;
  let f = match ast.data {
    syn::Data::Struct(ds) => match ds.fields {
      syn::Fields::Named(fields) => fields.named.iter().map(|f| f.ident.unwrap())
      ,_ => panic!("{} has no named fields", name)
    }
    ,_ => panic!("{} is not a struct", &name)
  };

  let res = quote! {
    impl QueryParams for #name {
      fn to_hashmap(&self) -> HashMap<String, To_Sql> {
        let params: HashMap<String, To_Sql> = HashMap::new();
        #(
          if let Some(v) = self.#f { params.push(v) }
        )*
        params
      }
    }
  };

  res.into()
}