trait_eval
We all know Rust's trait system is Turing complete, so tell me, why aren't we exploiting this??? Who needs const-fn when we've got a crate like this?!
Honestly, I was too preoccupied with the fact that I could to stop to think whether I actually should.
Believe it or not, I even wrote docs for this.
Example
Here's an eminently readable example where we play FizzBuzz at compile-time!
trait FizzBuzzType {
fn show() -> String; // Don't worry about this -- it's just so we can print the result
}
struct Fizz;
impl FizzBuzzType for Fizz {
fn show() -> String {
"Fizz".to_string()
}
}
struct Buzz;
impl FizzBuzzType for Buzz {
fn show() -> String {
"Buzz".to_string()
}
}
struct FizzBuzz;
impl FizzBuzzType for FizzBuzz {
fn show() -> String {
"FizzBuzz".to_string()
}
}
impl<T: Nat> FizzBuzzType for T
where
T: Eval,
<T as Eval>::Output: Display,
{
fn show() -> String {
format!("{}", T::eval())
}
}
trait FizzBuzzEval: Nat {
type Result: FizzBuzzType;
}
impl<T: Nat,
Mod3: Nat,
Mod5: Nat,
ShouldFizz: Bool,
ShouldBuzz: Bool,
ShouldFizzBuzz: Bool,
DidBuzz: FizzBuzzType,
DidFizz: FizzBuzzType,
DidFizzBuzz: FizzBuzzType> FizzBuzzEval for T
where
T: Mod<Three, Result = Mod3> + Mod<Five, Result = Mod5>,
Mod3: Equals<Zero, Result = ShouldFizz>,
Mod5: Equals<Zero, Result = ShouldBuzz>,
ShouldFizz: AndAlso<ShouldBuzz, Result = ShouldFizzBuzz>,
(Fizz, T): If<ShouldFizz, Result = DidFizz>,
(Buzz, DidFizz): If<ShouldBuzz, Result = DidBuzz>,
(FizzBuzz, DidBuzz): If<ShouldFizzBuzz, Result = DidFizzBuzz>,
{
type Result = DidFizzBuzz;
}
assert_eq!(<One as FizzBuzzEval>::Result::show(), "1");
assert_eq!(<Two as FizzBuzzEval>::Result::show(), "2");
assert_eq!(<Three as FizzBuzzEval>::Result::show(), "Fizz");
assert_eq!(<Four as FizzBuzzEval>::Result::show(), "4");
assert_eq!(<Five as FizzBuzzEval>::Result::show(), "Buzz");
assert_eq!(<Six as FizzBuzzEval>::Result::show(), "Fizz");
assert_eq!(<Seven as FizzBuzzEval>::Result::show(), "7");
assert_eq!(<Eight as FizzBuzzEval>::Result::show(), "8");
assert_eq!(<Nine as FizzBuzzEval>::Result::show(), "Fizz");
assert_eq!(<Ten as FizzBuzzEval>::Result::show(), "Buzz");
type Fifteen = <Three as Times<Five>>::Result;
assert_eq!(<Fifteen as FizzBuzzEval>::Result::show(), "FizzBuzz"); // !!!Contributing
Please, for the love of God, don't use this crate. If you must contribute, open a PR.
Projects using this crate
Some people never listen, huh?
- fortraith - Forth implemented in the Rust trait system