1 //! [![github]](https://github.com/dtolnay/enumn) [![crates-io]](https://crates.io/crates/enumn) [![docs-rs]](https://docs.rs/enumn)
2 //!
3 //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
4 //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
5 //! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
6 //!
7 //! <br>
8 //!
9 //! Convert number to enum.
10 //!
11 //! This crate provides a derive macro to generate a function for converting a
12 //! primitive integer into the corresponding variant of an enum.
13 //!
14 //! The generated function is named `n` and has the following signature:
15 //!
16 //! ```
17 //! # const IGNORE: &str = stringify! {
18 //! impl YourEnum {
19 //! pub fn n(value: Repr) -> Option<Self>;
20 //! }
21 //! # };
22 //! ```
23 //!
24 //! where `Repr` is an integer type of the right size as described in more
25 //! detail below.
26 //!
27 //! # Example
28 //!
29 //! ```
30 //! use enumn::N;
31 //!
32 //! #[derive(PartialEq, Debug, N)]
33 //! enum Status {
34 //! LegendaryTriumph,
35 //! QualifiedSuccess,
36 //! FortuitousRevival,
37 //! IndeterminateStalemate,
38 //! RecoverableSetback,
39 //! DireMisadventure,
40 //! AbjectFailure,
41 //! }
42 //!
43 //! fn main() {
44 //! let s = Status::n(1);
45 //! assert_eq!(s, Some(Status::QualifiedSuccess));
46 //!
47 //! let s = Status::n(9);
48 //! assert_eq!(s, None);
49 //! }
50 //! ```
51 //!
52 //! # Signature
53 //!
54 //! The generated signature depends on whether the enum has a `#[repr(..)]`
55 //! attribute. If a `repr` is specified, the input to `n` will be required to be
56 //! of that type.
57 //!
58 //! ```
59 //! #[derive(enumn::N)]
60 //! # enum E0 {
61 //! # IGNORE
62 //! # }
63 //! #
64 //! #[repr(u8)]
65 //! enum E {
66 //! /* ... */
67 //! # IGNORE
68 //! }
69 //!
70 //! // expands to:
71 //! impl E {
72 //! pub fn n(value: u8) -> Option<Self> {
73 //! /* ... */
74 //! # unimplemented!()
75 //! }
76 //! }
77 //! ```
78 //!
79 //! On the other hand if no `repr` is specified then we get a signature that is
80 //! generic over a variety of possible types.
81 //!
82 //! ```
83 //! # enum E {}
84 //! #
85 //! impl E {
86 //! pub fn n<REPR: Into<i64>>(value: REPR) -> Option<Self> {
87 //! /* ... */
88 //! # unimplemented!()
89 //! }
90 //! }
91 //! ```
92 //!
93 //! # Discriminants
94 //!
95 //! The conversion respects explicitly specified enum discriminants. Consider
96 //! this enum:
97 //!
98 //! ```
99 //! #[derive(enumn::N)]
100 //! enum Letter {
101 //! A = 65,
102 //! B = 66,
103 //! }
104 //! ```
105 //!
106 //! Here `Letter::n(65)` would return `Some(Letter::A)`.
107
108 #![doc(html_root_url = "https://docs.rs/enumn/0.1.14")]
109 #![allow(
110 clippy::missing_panics_doc,
111 clippy::needless_doctest_main,
112 clippy::single_match_else
113 )]
114
115 extern crate proc_macro;
116
117 use proc_macro::TokenStream;
118 use quote::quote;
119 use syn::{parse_macro_input, Data, DeriveInput, Error, Fields, Ident};
120
121 #[proc_macro_derive(N)]
derive(input: TokenStream) -> TokenStream122 pub fn derive(input: TokenStream) -> TokenStream {
123 let input = parse_macro_input!(input as DeriveInput);
124
125 let variants = match input.data {
126 Data::Enum(data) => data.variants,
127 Data::Struct(_) | Data::Union(_) => panic!("input must be an enum"),
128 };
129
130 for variant in &variants {
131 match variant.fields {
132 Fields::Unit => {}
133 Fields::Named(_) | Fields::Unnamed(_) => {
134 let span = variant.ident.span();
135 let err = Error::new(span, "enumn: variant with data is not supported");
136 return err.to_compile_error().into();
137 }
138 }
139 }
140
141 // Parse repr attribute like #[repr(u16)].
142 let mut repr = None;
143 for attr in input.attrs {
144 if attr.path().is_ident("repr") {
145 if let Ok(name) = attr.parse_args::<Ident>() {
146 match name.to_string().as_str() {
147 "u8" | "u16" | "u32" | "u64" | "u128" | "usize" | "i8" | "i16" | "i32"
148 | "i64" | "i128" | "isize" => {
149 repr = Some(quote!(#name));
150 }
151 _ => {}
152 }
153 }
154 }
155 }
156
157 let signature;
158 let value;
159 match repr {
160 Some(ref repr) => {
161 signature = quote! {
162 fn n(value: #repr)
163 };
164 value = quote!(value);
165 }
166 None => {
167 repr = Some(quote!(i64));
168 signature = quote! {
169 fn n<REPR: Into<i64>>(value: REPR)
170 };
171 value = quote! {
172 <REPR as Into<i64>>::into(value)
173 };
174 }
175 }
176
177 let ident = input.ident;
178 let declare_discriminants = variants.iter().map(|variant| {
179 let variant = &variant.ident;
180 quote! {
181 const #variant: #repr = #ident::#variant as #repr;
182 }
183 });
184 let match_discriminants = variants.iter().map(|variant| {
185 let variant = &variant.ident;
186 quote! {
187 discriminant::#variant => Some(#ident::#variant),
188 }
189 });
190
191 TokenStream::from(quote! {
192 impl #ident {
193 pub #signature -> Option<Self> {
194 #[allow(non_camel_case_types)]
195 struct discriminant;
196 #[allow(non_upper_case_globals)]
197 impl discriminant {
198 #(#declare_discriminants)*
199 }
200 match #value {
201 #(#match_discriminants)*
202 _ => None,
203 }
204 }
205 }
206 })
207 }
208