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extern crate proc_macro;
use proc_macro::TokenStream;
use syn::{
Data,
Fields,
};
use quote::quote;
#[proc_macro_derive(NewType)]
pub fn newtype(input: TokenStream) -> TokenStream {
let input = syn::parse::<syn::DeriveInput>(input).expect("syn parse derive input");
gen_impl(input).into()
}
fn gen_impl(input: syn::DeriveInput) -> proc_macro2::TokenStream {
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let name = input.ident;
let st = match input.data {
Data::Struct(st) => st,
_ => panic!("NewType can only be derived for single-field tuple structs"),
};
let fields = match st.fields {
Fields::Unnamed(fields) => fields,
_ => panic!("NewType can only be derived for single-field tuple structs"),
};
if fields.unnamed.len() != 1 {
panic!("NewType can only be derived for single-field tuple structs")
}
let field_ty = fields.unnamed.into_iter().nth(0).unwrap().ty;
let from = quote! {
impl #impl_generics From<#field_ty> for #name #ty_generics #where_clause {
fn from(other: #field_ty) -> #name #ty_generics {
#name (other)
}
}
};
let deref = quote! {
impl #impl_generics ::core::ops::Deref for #name #ty_generics #where_clause {
type Target = #field_ty;
fn deref(&self) -> &Self::Target {
&self.0
}
}
};
let deref_mut = quote! {
impl #impl_generics ::core::ops::DerefMut for #name #ty_generics #where_clause {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
};
let into_inner = quote! {
impl #impl_generics #name #ty_generics #where_clause {
pub fn into_inner(self) -> #field_ty {
self.0
}
}
};
quote! {
#from #deref #deref_mut #into_inner
}
}