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#![recursion_limit = "128"]
extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;
use std::iter;
use proc_macro::TokenStream;
use syn::{Body, Ident, Variant, VariantData};
use quote::Tokens;
fn generate_enum_code(name: &Ident, variants: &[Variant]) -> Tokens {
let mut enum_count = 0usize;
for &Variant {
ref data,
ref discriminant,
..
} in variants {
if data != &VariantData::Unit {
panic!("#[derive(EnumMap)] requires C style style enum");
}
if discriminant.is_some() {
panic!("#[derive(EnumMap)] doesn't currently support discriminants");
}
enum_count += 1;
}
let variant_a = variants.iter().map(|variant| &variant.ident);
let variant_b = variants.iter().map(|variant| &variant.ident);
let repeat_name_a = iter::repeat(name).take(variants.len());
let repeat_name_b = repeat_name_a.clone();
let counter = 0..variants.len();
let to_usize = if variants.len() == 0 {
quote! { unreachable!() }
} else {
quote! { self as usize }
};
quote! {
impl<V> ::enum_map::Internal<V> for #name {
type Array = [V; #enum_count];
fn slice(array: &Self::Array) -> &[V] {
array
}
fn slice_mut(array: &mut Self::Array) -> &mut [V] {
array
}
fn from_usize(value: usize) -> Self {
match value {
#(
#counter => #repeat_name_a::#variant_a,
)*
_ => unreachable!()
}
}
fn to_usize(self) -> usize {
#to_usize
}
fn from_function<F: FnMut(Self) -> V>(mut f: F) -> Self::Array {
[#(
f(#repeat_name_b::#variant_b),
)*]
}
}
}
}
#[proc_macro_derive(EnumMap)]
pub fn derive_enum_map(input: TokenStream) -> TokenStream {
let input = syn::parse_macro_input(&input.to_string()).unwrap();
match input.body {
Body::Enum(ref variants) => generate_enum_code(&input.ident, variants),
_ => panic!("#[derive(EnumMap)] is only defined for enums"),
}
.parse()
.unwrap()
}