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|
//! Support for `#[derive(Rand)]`
//!
//! # Examples
//!
//! ```
//! extern crate rand;
//! #[macro_use]
//! extern crate rand_derive;
//!
//! #[derive(Rand, Debug)]
//! struct MyStruct {
//! a: i32,
//! b: u32,
//! }
//!
//! fn main() {
//! println!("{:?}", rand::random::<MyStruct>());
//! }
//! ```
extern crate proc_macro;
#[macro_use]
extern crate quote;
extern crate syn;
use proc_macro::TokenStream;
#[proc_macro_derive(Rand)]
pub fn rand_derive(input: TokenStream) -> TokenStream {
let s = input.to_string();
let ast = syn::parse_derive_input(&s).unwrap();
let gen = impl_rand_derive(&ast);
gen.parse().unwrap()
}
fn impl_rand_derive(ast: &syn::MacroInput) -> quote::Tokens {
let name = &ast.ident;
let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
let rand = match ast.body {
syn::Body::Struct(syn::VariantData::Struct(ref body)) => {
let fields = body
.iter()
.filter_map(|field| field.ident.as_ref())
.map(|ident| quote! { #ident: __rng.gen() })
.collect::<Vec<_>>();
quote! { #name { #(#fields,)* } }
},
syn::Body::Struct(syn::VariantData::Tuple(ref body)) => {
let fields = (0..body.len())
.map(|_| quote! { __rng.gen() })
.collect::<Vec<_>>();
quote! { #name (#(#fields),*) }
},
syn::Body::Struct(syn::VariantData::Unit) => {
quote! { #name }
},
syn::Body::Enum(ref body) => {
if body.is_empty() {
panic!("`Rand` cannot be derived for enums with no variants");
}
let len = body.len();
let mut arms = body
.iter()
.map(|variant| {
let ident = &variant.ident;
match variant.data {
syn::VariantData::Struct(ref body) => {
let fields = body
.iter()
.filter_map(|field| field.ident.as_ref())
.map(|ident| quote! { #ident: __rng.gen() })
.collect::<Vec<_>>();
quote! { #name::#ident { #(#fields,)* } }
},
syn::VariantData::Tuple(ref body) => {
let fields = (0..body.len())
.map(|_| quote! { __rng.gen() })
.collect::<Vec<_>>();
quote! { #name::#ident (#(#fields),*) }
},
syn::VariantData::Unit => quote! { #name::#ident }
}
});
match len {
1 => quote! { #(#arms)* },
2 => {
let (a, b) = (arms.next(), arms.next());
quote! { if __rng.gen() { #a } else { #b } }
},
_ => {
let mut variants = arms
.enumerate()
.map(|(index, arm)| quote! { #index => #arm })
.collect::<Vec<_>>();
variants.push(quote! { _ => unreachable!() });
quote! { match __rng.gen_range(0, #len) { #(#variants,)* } }
},
}
}
};
quote! {
impl #impl_generics ::rand::Rand for #name #ty_generics #where_clause {
#[inline]
fn rand<__R: ::rand::Rng>(__rng: &mut __R) -> Self {
#rand
}
}
}
}
|
