vendor/derive_more/src/sum_like.rs

   1 use crate::utils::{
   2     add_extra_ty_param_bound, add_extra_where_clauses, MultiFieldData, State,
   3 };
   4 use proc_macro2::{Span, TokenStream};
   5 use quote::quote;
   6 use syn::{DeriveInput, Ident, Result};
   7
   8 pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
   9     let state = State::new(
  10         input,
  11         trait_name,
  12         quote!(::core::iter),
  13         trait_name.to_lowercase(),
  14     )?;
  15     let multi_field_data = state.enabled_fields_data();
  16     let MultiFieldData {
  17         input_type,
  18         field_types,
  19         trait_path,
  20         method_ident,
  21         ..
  22     } = multi_field_data.clone();
  23
  24     let op_trait_name = if trait_name == "Sum" { "Add" } else { "Mul" };
  25     let op_trait_ident = Ident::new(op_trait_name, Span::call_site());
  26     let op_path = quote!(::core::ops::#op_trait_ident);
  27     let op_method_ident =
  28         Ident::new(&(op_trait_name.to_lowercase()), Span::call_site());
  29     let has_type_params = input.generics.type_params().next().is_none();
  30     let generics = if has_type_params {
  31         input.generics.clone()
  32     } else {
  33         let (_, ty_generics, _) = input.generics.split_for_impl();
  34         let generics = add_extra_ty_param_bound(&input.generics, trait_path);
  35         let operator_where_clause = quote! {
  36             where #input_type#ty_generics: #op_path<Output=#input_type#ty_generics>
  37         };
  38         add_extra_where_clauses(&generics, operator_where_clause)
  39     };
  40     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
  41
  42     let initializers: Vec<_> = field_types
  43         .iter()
  44         .map(|field_type| quote!(#trait_path::#method_ident(::core::iter::empty::<#field_type>())))
  45         .collect();
  46     let identity = multi_field_data.initializer(&initializers);
  47
  48     Ok(quote!(
  49         impl#impl_generics #trait_path for #input_type#ty_generics #where_clause {
  50             #[inline]
  51             fn #method_ident<I: ::core::iter::Iterator<Item = Self>>(iter: I) -> Self {
  52                 iter.fold(#identity, #op_path::#op_method_ident)
  53             }
  54         }
  55     ))
  56 }