Simple Dependency Injection

di.rs

#![feature(existential_type)]

type Result<T> = std::result::Result<T, failure::Error>;

trait MyTrait {
    fn greet(&self) -> String;
}

struct MyType {}

impl MyTrait for MyType {
    fn greet(&self) -> String {
        String::from("Hello, world!")
    }
}

trait Container {
    type MyTraitType: MyTrait;
    type MyFnType: Fn();
    
    fn resolve_my_trait() -> Self::MyTraitType;
    fn resolve_my_fn() -> Self::MyFnType;
}

struct MyContainer;

impl Container for MyContainer {
    existential type MyTraitType: MyTrait;
    existential type MyFnType: Fn();
    
    fn resolve_my_trait() -> Self::MyTraitType { MyType {} }
    fn resolve_my_fn() -> Self::MyFnType { || println!("Yay, works with Voldemort types!") }
}

fn main() -> Result<()> {
    let my_type = MyContainer::resolve_my_trait();
    println!("{}", my_type.greet());
    MyContainer::resolve_my_fn()();
    Ok(())
}