The macro-attr
modern fork.
This crate provides the macro_attr!
macro that enables the use of custom, macro-based attributes and derivations.
The macro_attr!
macro should be used to wrap an entire single item (enum
, struct
, etc.) declaration, including its attributes (both derive
and others). All attributes and derivations which whose names end with !
will be assumed to be implemented by macros, and treated accordingly.
use macro_attr_2018::macro_attr;
// Define some traits to be derived.
trait TypeName {
fn type_name() -> &'static str;
}
trait ReprType {
type Repr;
}
// Define macros which derive implementations of these macros.
macro_rules! TypeName {
// We can support any kind of item we want.
(() $vis:vis enum $name:ident $($tail:tt)+) => { TypeName! { @impl $name } };
(() $vis:vis struct $name:ident $($tail:tt)+) => { TypeName! { @impl $name } };
// Inner rule to cut down on repetition.
(@impl $name:ident) => {
impl TypeName for $name {
fn type_name() -> &'static str { stringify!($name) }
}
};
}
macro_rules! ReprType {
// Note that we use a "derivation argument" here for the `$repr` type.
(($repr:ty) $vis:vis enum $name:ident $($tail:tt)+) => {
impl ReprType for $name {
type Repr = $repr;
}
};
}