macro-attr-2018

The macro-attr modern fork.

This crate provides the macro_attr! macro that enables the use of custom, macro-based 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 derivations which whose names end with ! will be assumed to be implemented by macros, and treated accordingly.

```rust use macroattr2018::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; } }; }

// Derive.

macro_attr! { #[derive(TypeName!, ReprType!(u16))] #[repr(u16)] enum SomeEnum { A, B, C, D } } ```