derive_more/
index.rs

1use crate::utils::{add_where_clauses_for_new_ident, SingleFieldData, State};
2use proc_macro2::{Span, TokenStream};
3use quote::quote;
4use syn::{parse::Result, DeriveInput, Ident};
5
6/// Provides the hook to expand `#[derive(Index)]` into an implementation of `Index`
7pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
8    let index_type = &Ident::new("__IdxT", Span::call_site());
9    let mut state = State::with_field_ignore(
10        input,
11        trait_name,
12        quote!(::core::ops),
13        trait_name.to_lowercase(),
14    )?;
15    state.add_trait_path_type_param(quote!(#index_type));
16    let SingleFieldData {
17        field,
18        field_type,
19        input_type,
20        trait_path_with_params,
21        casted_trait,
22        member,
23        ..
24    } = state.assert_single_enabled_field();
25
26    let type_where_clauses = quote! {
27        where #field_type: #trait_path_with_params
28    };
29
30    let new_generics = add_where_clauses_for_new_ident(
31        &input.generics,
32        &[field],
33        index_type,
34        type_where_clauses,
35        true,
36    );
37
38    let (impl_generics, _, where_clause) = new_generics.split_for_impl();
39    let (_, ty_generics, _) = input.generics.split_for_impl();
40    Ok(quote! {
41        impl#impl_generics #trait_path_with_params for #input_type#ty_generics #where_clause
42        {
43            type Output = #casted_trait::Output;
44            #[inline]
45            fn index(&self, idx: #index_type) -> &Self::Output {
46                #casted_trait::index(&#member, idx)
47            }
48        }
49    })
50}
derive_more/index.rs

derive_more/
index.rs
