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-rw-r--r--rand/rand-derive/src/lib.rs116
1 files changed, 116 insertions, 0 deletions
diff --git a/rand/rand-derive/src/lib.rs b/rand/rand-derive/src/lib.rs
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+++ b/rand/rand-derive/src/lib.rs
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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
+ }
+ }
+ }
+}