/
macro_rules.rs
49 lines (43 loc) · 1.15 KB
/
macro_rules.rs
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// This is an example of using the proc_macro_rules crate to convert a macro_rules
// macro to a procedural one. The two macros should work in exactly the same way.
// The main differences are:
// * we must manually handle the token streams and their type conversion
// * we use the rules! macro
// * we use the quote! macro for each body (which requires using `#` instead of `$`)
#![allow(unused_macros)]
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro_rules::rules;
use quote::quote;
// Declarative version using macro_rules.
macro_rules! vec {
() => {
Vec::new()
};
( $( $x:expr ),+ ) => {
{
let mut temp_vec = Vec::new();
$(
temp_vec.push($x);
)*
temp_vec
}
};
}
// Procedural version.
#[proc_macro]
pub fn vec(input: TokenStream) -> TokenStream {
rules!(input.into() => {
() => { quote! {
Vec::new()
}}
( $( $x:expr ),+ ) => { quote! {
let mut temp_vec = Vec::new();
#(
temp_vec.push(#x);
)*
temp_vec
}}
})
.into()
}