2 releases
0.1.1 | Aug 22, 2023 |
---|---|
0.1.0 | Aug 22, 2023 |
#533 in Procedural macros
11KB
131 lines
Typemarker
Procedural macro for easily creating multiple linked marker types, useful for the typestate pattern.
Examples
By default, typemarker adds both a trait and a dynamic value for the marker enum called "Trait" and "Dynamic" respectively.
use core::marker::PhantomData;
use typemarker::typemarker;
#[typemarker]
enum LightColor {
Red,
Yellow,
Green,
}
struct TrafficLight<Color: LightColor::Trait>(PhantomData<Color>);
impl TrafficLight<LightColor::Red> {
fn turn_green(self) -> TrafficLight<LightColor::Green> {
TrafficLight::<LightColor::Green>(PhantomData)
}
}
impl<Color: LightColor::Trait> TrafficLight<Color> {
fn can_go(&self) -> bool {
Color::dynamic() == LightColor::Dynamic::Green
}
}
let light = TrafficLight::<LightColor::Red>(PhantomData);
assert!(!light.can_go());
let light = light.turn_green();
assert!(light.can_go());
Both the trait and the dynamic value can be disabled using no_value
and no_trait
respectively.
use core::marker::PhantomData;
use typemarker::typemarker;
#[typemarker(no_value, no_trait)]
enum LightColor {
Red,
Yellow,
Green,
}
// Compile error, LightColor::Trait does not exist on no_trait.
// struct TrafficLight<Color: LightColor::Trait>(PhantomData<Color>);
struct TrafficLight<Color>(PhantomData<Color>);
impl TrafficLight<LightColor::Red> {
fn turn_green(self) -> TrafficLight<LightColor::Green> {
TrafficLight::<LightColor::Green>(PhantomData)
}
}
// Compile error, dynamic doesn't exist on no_value.
// impl<Color: LightColor::Trait> TrafficLight<Color> {
// fn can_go(&self) -> bool {
// Color::dynamic() == LightColor::Dynamic::Green
// }
// }
let light = TrafficLight::<LightColor::Red>(PhantomData);
light.turn_green();
They can also be renamed using trait_name = ...
and value_name = ...
:
use core::marker::PhantomData;
use typemarker::typemarker;
#[typemarker(trait_name = TraitName, value_name = ValueName)]
enum LightColor {
Red,
Yellow,
Green,
}
struct TrafficLight<Color: LightColor::TraitName>(PhantomData<Color>);
impl TrafficLight<LightColor::Red> {
fn turn_green(self) -> TrafficLight<LightColor::Green> {
TrafficLight::<LightColor::Green>(PhantomData)
}
}
impl<Color: LightColor::TraitName> TrafficLight<Color> {
fn can_go(&self) -> bool {
Color::dynamic() == LightColor::ValueName::Green
}
}
let light = TrafficLight::<LightColor::Red>(PhantomData);
assert!(!light.can_go());
let light = light.turn_green();
assert!(light.can_go());
Dependencies
~0.6–1MB
~25K SLoC