Crate declarative_enum_dispatch

Declarative generation of enum dispatch

Generate boilerplate code for dynamic dispatch of a trait using an enum. Also generates From for every enum variant

This is a fully declarative version of enum_dispatch macro

For benchmarks look at enum_dispatch benchmarks crate

Usage example:

use declarative_enum_dispatch::enum_dispatch;

enum_dispatch!(
    pub trait ShapeTrait: Clone + std::fmt::Debug + 'static {
        /// No return + default implementation
        fn print_name(&self) {
            println!("name: `{}`", self.name());
        }
        /// Basic call without arguments
        fn name(&self) -> String;
        fn area(&self) -> i32;

        /// Mutable self + arguments
        fn grow(&mut self, numerator: i32, denominator: i32,);

        /// Kinda supports generics :) Bot not generic parameters, only `impl Trait`
        fn greater(&self, other: &impl ShapeTrait) -> bool;

        /// Supports async methods
        async fn send(&self);

        /// Works with attributes
        #[cfg(feature = "platform_specific")]
        fn platform_specific(self);
    }

    #[derive(Debug, Clone)]
    pub enum Shape {
        Rect(Rect),
        Circle(Circle),
        #[cfg(feature = "platform_specific")]
        Cube(Cube)
    }
);
#[derive(Debug, Clone)]
pub struct Rect{ w: i32, h: i32 }
#[derive(Debug, Clone)]
pub struct Circle { r: i32 }

impl ShapeTrait for Rect {
    fn print_name(&self) {
        println!("rect name: `{}`", self.name());
    }
    fn name(&self) -> String {
        "Rect".to_string()
    }

    fn area(&self) -> i32 {
        self.w * self.h
    }

    fn grow(&mut self, numerator: i32, denominator: i32) {
        self.w = self.w * numerator / denominator;
        self.h = self.h * numerator / denominator;
    }

    fn greater(&self, other: &impl ShapeTrait) -> bool {
        self.area() > other.area()
    }

    async fn send(&self) {}
}

impl ShapeTrait for Circle {
    fn name(&self) -> String {
        "Circle".to_string()
    }

    fn area(&self) -> i32 {
        // close enough PI approximation :)
        3 * self.r * self.r
    }

    fn grow(&mut self, numerator: i32, denominator: i32 ) {
        self.r = self.r * numerator / denominator;
    }

    fn greater(&self, other: &impl ShapeTrait) -> bool {
        self.area() > other.area()
    }

    async fn send(&self) {}
}


assert_eq!(Shape::Rect(Rect { w: 1, h: 1 }).name(), "Rect".to_string());
assert_eq!(Shape::Circle(Circle { r: 1 }).name(), "Circle".to_string());

Macro expansion

Expansion of the macro above

use declarative_enum_dispatch::enum_dispatch;
pub trait ShapeTrait: Clone + std::fmt::Debug + 'static {
    /// No return + default implementation
    fn print_name(&self) {
        println!("name: `{}`", self.name());
    }
    /// Basic call without arguments
    fn name(&self) -> String;
    fn area(&self) -> i32;
    /// Mutable self + arguments
    fn grow(&mut self, numerator: i32, denominator: i32);
    /// Kinda supports generics :) Bot not generic parameters, only `impl Trait`
    fn greater(&self, other: &impl ShapeTrait) -> bool;
    /// Supports async methods
    async fn send(&self);
    /// Works with attributes
    #[cfg(feature = "platform_specific")]
    fn platform_specific(self);
}
#[derive(Debug, Clone)]
pub enum Shape {
    Rect(Rect),
    Circle(Circle),
    #[cfg(feature = "platform_specific")]
    Cube(Cube),
}
impl ShapeTrait for Shape {
    /// No return + default implementation
    fn print_name(&self) {
        match self {
            Shape::Rect(v) => v.print_name(),
            Shape::Circle(v) => v.print_name(),
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.print_name(),
        }
    }
    /// Basic call without arguments
    fn name(&self) -> String {
        match self {
            Shape::Rect(v) => v.name(),
            Shape::Circle(v) => v.name(),
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.name(),
        }
    }
    fn area(&self) -> i32 {
        match self {
            Shape::Rect(v) => v.area(),
            Shape::Circle(v) => v.area(),
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.area(),
        }
    }
    /// Mutable self + arguments
    fn grow(&mut self, numerator: i32, denominator: i32) {
        match self {
            Shape::Rect(v) => v.grow(numerator, denominator),
            Shape::Circle(v) => v.grow(numerator, denominator),
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.grow(numerator, denominator),
        }
    }
    /// Kinda supports generics :) Bot not generic parameters, only `impl Trait`
    fn greater(&self, other: &impl ShapeTrait) -> bool {
        match self {
            Shape::Rect(v) => v.greater(other),
            Shape::Circle(v) => v.greater(other),
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.greater(other),
        }
    }
    /// Supports async methods
    async fn send(&self) {
        match self {
            Shape::Rect(v) => v.send().await,
            Shape::Circle(v) => v.send().await,
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.send().await,
        }
    }
    /// Works with attributes
    #[cfg(feature = "platform_specific")]
    fn platform_specific(self) {
        match self {
            Shape::Rect(v) => v.platform_specific(),
            Shape::Circle(v) => v.platform_specific(),
            #[cfg(feature = "platform_specific")]
            Shape::Cube(v) => v.platform_specific(),
        }
    }
}
impl From<Rect> for Shape {
    fn from(value: Rect) -> Shape {
        Shape::Rect(value)
    }
}
impl From<Circle> for Shape {
    fn from(value: Circle) -> Shape {
        Shape::Circle(value)
    }
}
#[cfg(feature = "platform_specific")]
impl From<Cube> for Shape {
    fn from(value: Cube) -> Shape {
        Shape::Cube(value)
    }
}

Macros

enum_dispatch