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extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;
use proc_macro::{TokenStream};
use syn::{
Body, Ident, VariantData, PolyTraitRef, Ty, TyParamBound,
TraitBoundModifier, WherePredicate, WhereBoundPredicate
};
use quote::Tokens;
#[proc_macro_derive(Construct)]
pub fn construct(input: TokenStream) -> TokenStream {
let s = input.to_string();
let ast = syn::parse_derive_input(&s).unwrap();
let gen = impl_construct(&ast);
gen.parse().unwrap()
}
fn impl_construct(ast: &syn::DeriveInput) -> quote::Tokens {
if let Body::Struct(ref body) = ast.body {
let name = &ast.ident;
let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
let fields: Vec<(_, Ty)> = if let &VariantData::Struct(ref fields) = body {
fields.iter()
.map(|field| (
field.ident.as_ref().unwrap(),
field.ty.clone(),
)).collect()
} else {
panic!("Expected struct fields");
};
let mut where_clause = where_clause.clone();
let mut offsets = Tokens::new();
let mut i = 0;
let mut ns = vec![];
for &(_, ref ty) in &fields {
let ty_ident = if let &Ty::Path(_, ref parameters) = ty {
parameters.segments[0].ident.clone()
} else {
panic!("Could not find type identifier.")
};
if ty_ident != &Ident::new("u64") {
where_clause.predicates.push(WherePredicate::BoundPredicate(WhereBoundPredicate {
bound_lifetimes: vec![],
bounded_ty: ty.clone(),
bounds: vec![TyParamBound::Trait(PolyTraitRef {
bound_lifetimes: vec![],
trait_ref: Ident::new("Construct").into()
}, TraitBoundModifier::None)]
}));
offsets.append(
format!("let n{} = <{} as Construct>::n();", i, ty_ident)
);
i += 1;
} else {
ns.push(i);
}
}
let mut field_tokens = Tokens::new();
let mut i = 0;
for &(ref field, ref ty) in &fields {
field_tokens.append(field);
field_tokens.append(":");
let ty_ident = if let &Ty::Path(_, ref parameters) = ty {
parameters.segments[0].ident.clone()
} else {
panic!("Could not find type identifier.")
};
if ty_ident == &Ident::new("u64") {
field_tokens.append("vs[");
if ns[i] != 0 {
field_tokens.append(format!("n{}+", ns[i]-1));
}
field_tokens.append(&format!("{}", i));
field_tokens.append("]");
i += 1;
} else {
field_tokens.append("Construct::construct(vs)");
}
field_tokens.append(",");
}
quote! {
impl #impl_generics Construct for #name #ty_generics #where_clause {
fn construct(vs: &[u64]) -> Self {
#offsets
#name {
#field_tokens
}
}
}
}
} else {panic!("Must be a struct.")}
}