Code shared from the Rust Playground

playground.rs

#![feature(specialization)]

use std::any::type_name;


fn main(){
    let _:String=false.cast();
    let _:u32=0u8.cast();
}


impl As<String> for bool{
    fn as_(self)->String{
        if self { "true" }else{ "false" }.into()
    }
}



pub trait Cast<T> {
    fn cast(self) -> T;
}

pub trait As<T> {
    fn as_(self) -> T;
}

pub struct True;
pub struct False;


pub trait DoesItImplInto<T>{
    type DoesIt;
}

default impl<This,T> DoesItImplInto<T> for This{
    type DoesIt=False;
}

impl<This,T> DoesItImplInto<T> for This
where
    This:Into<T>,
{
    type DoesIt=True;
}

pub trait CastInner<ImplsInto,T>{
    fn _cast_inner(self) -> T;
}

impl<This,T> CastInner<True,T> for This
where
    This:Into<T>,
{
    fn _cast_inner(self) -> T{
        println!("{}:Into<{}>",type_name::<This>(),type_name::<T>());
        self.into()
    }
}

impl<This,T> CastInner<False,T> for This
where
    This:As<T>,
{
    fn _cast_inner(self) -> T{
        println!("{}:As<{}>",type_name::<This>(),type_name::<T>());
        self.as_()
    }
}


impl<X, T> Cast<T> for X
where
    X: DoesItImplInto<T>,
    X: CastInner<
        <X as DoesItImplInto<T>>::DoesIt,
        T,
    >
{
    fn cast(self) -> T {
        CastInner::_cast_inner(self)
    }
}