Attribute Macro macro_rules_derive

#[macro_rules_derive]

Applies the given macro_rules! macro to the decorated item.

This, as with any #[derive(...)], does not consume the item it decorates: instead, it only generates code on top of it.

Examples

Implementing Into<Int> for a given #[repr(Int)] enum:

#[macro_use]
extern crate macro_rules_attribute;

macro_rules! ToInteger {(
   #[repr($Int:ident)]
   $(#[$enum_meta:meta])*
   $pub:vis
   enum $Enum:ident {
       $(
           $Variant:ident $(= $value:expr)?
       ),* $(,)?
   }
) => (
   impl ::core::convert::From<$Enum> for $Int {
       #[inline]
       fn from (x: $Enum)
         -> Self
       {
           x as _
       }
   }
)}

#[macro_rules_derive(ToInteger)] // or `#[macro_rules_derive(ToInteger!)]`
#[repr(u32)]
enum Bool {
   False,
   True,
}

fn main ()
{
   assert_eq!(u32::from(Bool::False), 0);
   assert_eq!(u32::from(Bool::True), 1);
   // assert_eq!(u8::from(Bool::False), 0);
   // ^ error[E0277]: the trait bound `u8: std::convert::From<main::Bool>` is not satisfied
}

Difference with #[derive]

#[macro_rules_derive] is specifically intended to be used with macro_rules!-based derives:

• it won’t accept classic derives;

• thanks to that, the trailing ! on the macro name is not mandatory.

For #[derive], it’s exactly the opposite.