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|
use proc_macro::{TokenStream, TokenTree};
use quote::quote;
/// Subtracts two numbers and calls a given callback macro with the result.
///
/// # Input
/// `number - number, callback`
///
/// # Examples
/// ```
/// # use std::any::TypeId;
/// use util_macros::sub;
///
/// macro_rules! sub_cb {
/// ($num: literal) => {
/// $num
/// };
/// }
///
/// type Foo = [u8; sub!(5 - 2, sub_cb)];
///
/// assert_eq!(TypeId::of::<Foo>(), TypeId::of::<[u8; 3]>());
/// ```
/// <br>
///
/// The callback is called with the identifier `overflow` if a overflow occurs.
/// ```
/// # use std::any::TypeId;
/// use util_macros::sub;
///
/// macro_rules! sub_cb {
/// ($num: literal) => {
/// $num
/// };
///
/// (overflow) => {
/// 128
/// };
/// }
///
/// type Foo = [u8; sub!(3 - 10, sub_cb)];
///
/// assert_eq!(TypeId::of::<Foo>(), TypeId::of::<[u8; 128]>());
/// ```
#[proc_macro]
pub fn sub(input: TokenStream) -> TokenStream
{
let mut input_tt_iter = input.into_iter();
let num_a = match input_tt_iter.next().unwrap() {
TokenTree::Literal(lit) => lit.to_string().parse::<u32>().unwrap(),
_ => {
panic!("Expected a number literal");
}
};
match input_tt_iter.next().unwrap() {
TokenTree::Punct(punct) if punct.as_char() == '-' => {}
_ => {
panic!("Expected a '-' token");
}
};
let num_b = match input_tt_iter.next().unwrap() {
TokenTree::Literal(lit) => lit.to_string().parse::<u32>().unwrap(),
_ => {
panic!("Expected a number literal");
}
};
match input_tt_iter.next().unwrap() {
TokenTree::Punct(punct) if punct.as_char() == ',' => {}
_ => {
panic!("Expected a ',' token");
}
};
let cb_ident = match input_tt_iter.next().unwrap() {
TokenTree::Ident(cb_ident) => {
proc_macro2::Ident::new(&cb_ident.to_string(), cb_ident.span().into())
}
_ => {
panic!("Expected a identifier");
}
};
let Some(subtracted) = num_a.checked_sub(num_b) else {
return quote! {
#cb_ident!(overflow)
}
.into();
};
let subtracted_lit = proc_macro2::Literal::u32_unsuffixed(subtracted);
quote! {
#cb_ident!(#subtracted_lit)
}
.into()
}
|
