fnum-derive 0.0.1

fnum derive macro
Documentation 
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
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131

extern crate proc_macro;
use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, ItemEnum};

#[proc_macro_derive(Fnum)]
pub fn derive_fnum(input: TokenStream) -> TokenStream {
    let item = parse_macro_input!(input as ItemEnum);
    let enum_name = item.ident;
    let variants = item.variants;

    let variant_idx_arms = variants.iter().enumerate().map(|(i, variant)| {
        let ident = &variant.ident;
        match &variant.fields {
            syn::Fields::Named(_) => {
                quote! {
                    #enum_name::#ident{..} => {#i}
                }
            }
            syn::Fields::Unnamed(fields) => {
                let fs = fields.unnamed.iter().map(|_| {
                    quote! {_}
                }).collect::<Vec<_>>();
                quote! {
                    #enum_name::#ident(#(#fs),*) => {#i}
                }
            }
            syn::Fields::Unit => {
                quote! {
                    #enum_name::#ident => {#i}
                }
            }
        }
    }).collect::<Vec<_>>();

    let uninit_variant_arms = variants.iter().enumerate().map(|(i, variant)| {
        let ident = &variant.ident;
        match &variant.fields {
            syn::Fields::Named(fields) => {
                let inits = fields.named.iter().map(|field| {
                    let name = field.ident.clone().unwrap(); // unwrap daijoubu?
                    quote! {
                        #name: ::std::mem::MaybeUninit::uninit().assume_init()
                    }
                }).collect::<Vec<_>>();
                quote! {
                    #i => #enum_name::#ident{#(#inits),*}
                }
            }
            syn::Fields::Unnamed(fields) => {
                let inits = fields.unnamed.iter().map(|_| quote! { ::std::mem::MaybeUninit::uninit().assume_init() }).collect::<Vec<_>>();
                quote! {
                    #i => #enum_name::#ident(#(#inits),*)
                }
            }
            syn::Fields::Unit => {
                quote! {
                    #i => #enum_name::#ident
                }
            }
        }
    }).collect::<Vec<_>>();

    let make_table = variants.iter().enumerate().map(|(i, variant)| {
        let ident = &variant.ident;
        let arm = match &variant.fields {
            syn::Fields::Named(fields) => {
                let field_idents = fields.named.iter().map(|field| field.ident.clone().unwrap()).collect::<Vec<_>>();
                let pointers = field_idents.iter().map(|i| quote! {right_pointer(#i)}).collect::<Vec<_>>();
                quote! {
                    #enum_name::#ident{#(#field_idents),*} => {[#(#pointers),*].iter().max().unwrap() - pointer(&e)}
                }
            }
            syn::Fields::Unnamed(fields) => {
                let field_idents = fields.unnamed.iter().enumerate().map(|(i, _)| {
                    quote::format_ident!("field{}", i)
                }).collect::<Vec<_>>();
                let pointers = field_idents.iter().map(|i| quote! {right_pointer(#i)}).collect::<Vec<_>>();
                quote! {
                    #enum_name::#ident(#(#field_idents),*) => {[#(#pointers),*].iter().max().unwrap() - pointer(&e)}
                }
            }
            syn::Fields::Unit => {
                quote! {
                    #enum_name::#ident => {2} // dame kamo
                }
            }
        };
        quote! {{
            let e = unsafe { #enum_name::uninit_variant(#i) };
            let size = match &e {
                #arm,
                _ => unreachable!()
            };
            ::std::mem::forget(e);
            size
        }}
    }).collect::<Vec<_>>();

    let variant_num = variants.len();
    let gen = quote! {
        impl ::fnum::Fnum for #enum_name {
            fn variant_count() -> usize {
                #variant_num
            }
            fn variant_index(&self) -> usize {
                match self {
                    #(#variant_idx_arms),*
                }
            }
            unsafe fn uninit_variant(idx: usize) -> Self {
                assert!(idx < Self::variant_count());
                match idx {
                    #(#uninit_variant_arms,)*
                    _ => unreachable!(),
                }
            }
            fn size_of_variant(idx: usize) -> usize {
                fn pointer<T>(t: &T) -> usize {
                    t as *const _ as usize
                }
                fn right_pointer<T>(t: &T) -> usize {
                    unsafe {(t as *const T).offset(1) as usize}
                }
                static TABLE: ::fnum::__Lazy<[usize; #variant_num]> = ::fnum::__Lazy::new(|| [#(#make_table),*]);
                (*TABLE)[idx]
            }
        }
    };
    gen.into()
}