| //! 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 |
| } |
| } |
| } |
| } |