kalosm_learning_macro/
lib.rs

1use proc_macro::TokenStream;
2use quote::quote;
3use syn::{parse_macro_input, DeriveInput};
4
5#[proc_macro_derive(Class)]
6pub fn derive_class(input: TokenStream) -> TokenStream {
7    // Parse the input tokens into a syntax tree
8    let input = parse_macro_input!(input as DeriveInput);
9
10    let enum_data = if let syn::Data::Enum(e) = input.data {
11        e
12    } else {
13        panic!("Class can only be derived for enums");
14    };
15    let ident = input.ident;
16
17    let classes = enum_data.variants.len() as u32;
18    let to_class = enum_data.variants.iter().enumerate().map(|(i, v)| {
19        let ident = &v.ident;
20        let i = i as u32;
21        quote! {
22            Self::#ident => #i,
23        }
24    });
25    let from_class = enum_data.variants.iter().enumerate().map(|(i, v)| {
26        let ident = &v.ident;
27        let i = i as u32;
28        quote! {
29            #i => Self::#ident,
30        }
31    });
32
33    let expanded = quote! {
34        impl Class for #ident {
35            const CLASSES: Option<u32> = Some(#classes);
36
37            fn to_class(&self) -> u32 {
38                match self {
39                    #( #to_class )*
40                }
41            }
42            fn from_class(class: u32) -> Self {
43                match class {
44                    #( #from_class )*
45                    _ => panic!("Invalid class"),
46                }
47            }
48        }
49    };
50
51    // Hand the output tokens back to the compiler
52    TokenStream::from(expanded)
53}
kalosm_learning_macro/lib.rs

kalosm_learning_macro/
lib.rs
