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use crate::utils::{
field_idents, get_field_types, named_to_vec, numbered_vars, unnamed_to_vec,
};
use proc_macro2::TokenStream;
use quote::quote;
use syn::{Data, DeriveInput, Field, Fields, Ident};
/// Provides the hook to expand `#[derive(Constructor)]` into an implementation of `Constructor`
pub fn expand(input: &DeriveInput, _: &str) -> TokenStream {
let input_type = &input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let ((body, vars), fields) = match input.data {
Data::Struct(ref data_struct) => match data_struct.fields {
Fields::Unnamed(ref fields) => {
let field_vec = unnamed_to_vec(fields);
(tuple_body(input_type, &field_vec), field_vec)
}
Fields::Named(ref fields) => {
let field_vec = named_to_vec(fields);
(struct_body(input_type, &field_vec), field_vec)
}
Fields::Unit => (struct_body(input_type, &[]), vec![]),
},
_ => panic!("Only structs can derive a constructor"),
};
let original_types = &get_field_types(&fields);
quote! {
#[allow(missing_docs)]
#[automatically_derived]
impl #impl_generics #input_type #ty_generics #where_clause {
#[inline]
pub const fn new(#(#vars: #original_types),*) -> #input_type #ty_generics {
#body
}
}
}
}
fn tuple_body(return_type: &Ident, fields: &[&Field]) -> (TokenStream, Vec<Ident>) {
let vars = &numbered_vars(fields.len(), "");
(quote! { #return_type(#(#vars),*) }, vars.clone())
}
fn struct_body(return_type: &Ident, fields: &[&Field]) -> (TokenStream, Vec<Ident>) {
let field_names: &Vec<Ident> =
&field_idents(fields).iter().map(|f| (**f).clone()).collect();
let vars = field_names;
let ret_vars = field_names.clone();
(quote! { #return_type{#(#field_names: #vars),*} }, ret_vars)
}