derive_more_impl/
index_mut.rs

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

derive_more_impl/
index_mut.rs
