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extern crate proc_macro;
use proc_macro2::TokenStream;
use quote::quote;
use syn::{
Data, DeriveInput, Fields, Generics, GenericParam, Ident,
parse_macro_input, parse_quote,
};
#[proc_macro_derive(AsTuple)]
pub fn derive_as_tuple(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = input.ident;
let mut generics = input.generics.clone();
generics.params.push(parse_quote!('__as_tuple));
let generics = add_bounds(generics);
let (impl_generics, _, _) = generics.split_for_impl();
let (_, ty_generics, where_clause) = input.generics.split_for_impl();
let tuple_type = tuple_gen(&input.data, TupleOptions::TypeSig { mutable: false });
let tuple_type_mut = tuple_gen(&input.data, TupleOptions::TypeSig { mutable: true });
let destructure_expr = destructure(&name, &input.data, false);
let destructure_expr_mut = destructure(&name, &input.data, true);
let expanded = quote! {
impl #impl_generics ::as_tuple::AsTuple<'__as_tuple> for #name #ty_generics #where_clause {
type Tuple = #tuple_type;
type TupleMut = #tuple_type_mut;
fn as_tuple(&'__as_tuple self) -> Self::Tuple {
#destructure_expr
}
fn as_tuple_mut(&'__as_tuple mut self) -> Self::TupleMut {
#destructure_expr_mut
}
}
};
proc_macro::TokenStream::from(expanded)
}
fn add_bounds(mut generics: Generics) -> Generics {
for param in &mut generics.params {
match *param {
GenericParam::Type(ref mut type_param) => {
type_param.bounds.push(parse_quote!('__as_tuple));
},
GenericParam::Lifetime(ref mut lifetime_param) => {
lifetime_param.bounds.push(parse_quote!('__as_tuple));
},
_ => (),
}
}
generics
}
#[derive(Debug)]
enum TupleOptions {
TypeSig { mutable: bool },
Binding,
Ref { mutable: bool },
}
fn tuple_gen(data: &Data, options: TupleOptions) -> TokenStream {
match *data {
Data::Struct(ref data) => {
match data.fields {
Fields::Named(ref fields) => {
let recurse = fields
.named
.iter()
.map(|f| match options {
TupleOptions::TypeSig { mutable } => if !mutable {
let ty = &f.ty;
quote! { &'__as_tuple #ty }
} else {
let ty = &f.ty;
quote! { &'__as_tuple mut #ty }
},
TupleOptions::Binding => {
let name = f.ident.as_ref().unwrap();
quote! { #name }
},
_ => unimplemented!(),
});
quote! { (#(#recurse),*) }
},
Fields::Unnamed(ref fields) => {
let recurse = fields
.unnamed
.iter()
.enumerate()
.map(|(i, f)| match options {
TupleOptions::TypeSig { mutable } => if !mutable {
let ty = &f.ty;
quote! { &'__as_tuple #ty }
} else {
let ty = &f.ty;
quote! { &'__as_tuple mut #ty }
},
TupleOptions::Binding => {
quote! { field_#i }
},
TupleOptions::Ref { mutable } => if !mutable {
quote! { &self.#i }
} else {
quote! { &mut self.#i }
},
});
quote! { (#(#recurse),*) }
},
Fields::Unit => quote!{ () },
}
},
Data::Enum(_) | Data::Union(_) => unimplemented!(),
}
}
fn destructure(name: &Ident, data_root: &Data, mutable: bool) -> TokenStream {
match *data_root {
Data::Struct(ref data) => {
match data.fields {
Fields::Named(ref fields) => {
let recurse = fields.named.iter().map(|f| if !mutable {
let name = f.ident.as_ref().unwrap();
quote! { ref #name }
} else {
let name = f.ident.as_ref().unwrap();
quote! { ref mut #name }
});
let tuple_bind = tuple_gen(data_root, TupleOptions::Binding);
quote! {
let #name { #(#recurse),* } = self;
#tuple_bind
}
},
Fields::Unnamed(_) => {
let tuple = tuple_gen(data_root, TupleOptions::Ref { mutable });
quote! { #tuple }
},
Fields::Unit => quote!{ () },
}
},
Data::Enum(_) | Data::Union(_) => unimplemented!(),
}
}