Attribute Macro macro_rules_attribute::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.

Example

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!)]
#[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
}