diff options
Diffstat (limited to 'rand/rand-derive/src')
-rw-r--r-- | rand/rand-derive/src/lib.rs | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/rand/rand-derive/src/lib.rs b/rand/rand-derive/src/lib.rs new file mode 100644 index 0000000..80c803a --- /dev/null +++ b/rand/rand-derive/src/lib.rs @@ -0,0 +1,116 @@ +//! 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 + } + } + } +} |