vtable.rs

use std::{any::Any, collections::HashMap};

trait VTable<G = ()> {
    const NAME: &'static str;

    fn table(&self) -> HashMap<&str, &'static dyn Any>;
    fn get<T: 'static>(&self, name: &str) -> &T {
        let table = self.table();
        let any = table[name];

        any.downcast_ref().unwrap()
    }
}

struct Foo<T> {
    value: T
}

impl VTable<(u8,)> for Foo<u8> {
    const NAME: &'static str = "Foo";

    fn table(&self) -> HashMap<&str, &'static dyn Any> {
        let mut map = HashMap::<&str, &'static dyn Any>::new();

        map.insert("incr", &(foo_incr as fn(&mut Self)) as &dyn Any);

        map
    }
}

impl VTable<(String,)> for Foo<String> {
    const NAME: &'static str = "Foo";

    fn table(&self) -> HashMap<&str, &'static dyn Any> {
        let mut map = HashMap::<&str, &'static dyn Any>::new();

        map.insert("push_str", &(foo_push_str as fn(&mut Self, &str)) as &dyn Any);

        map
    }
}

fn foo_incr(this: &mut Foo<u8>) {
    this.value += 1;
}

fn foo_push_str(this: &mut Foo<String>, value: &str) {
    this.value.push_str(value)
}

fn main() {
    let mut foo = Foo {
        value: 1
    };

    foo.get::<fn(&mut Foo<u8>)>("incr")(&mut foo);

    println!("{}", foo.value);

    let mut foo2 = Foo {
        value: "asdasd".to_string()
    };

    foo2.get::<fn(&mut Foo<String>, &str)>("push_str")(&mut foo2, "qwe");

    println!("{}", foo2.value);
}