1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
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 variants = body
.iter()
.enumerate()
.map(|(index, variant)| {
let ident = &variant.ident;
let arm = 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 }
};
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
}
}
}
}