Expand description
§Compile-Time Evaluation
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?!
§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"); // !!!Structs§
Traits§
- AndAlso
- Logical And
- Bool
- The bool type (
true,false) - Equals
- Equality testing
- Eval
trait_evalto Rust conversion- Fact
- Factorial!
- Fib
- Built-in Fibonacci sequence
- If
- Conditional execution!
- Less
Than - Integer comparison
- Minus
- Saturating Subtraction
- Mod
- Remainders
- Nat
- The type of natural numbers (
0..) - Not
- Logical Not
- OrElse
- Logical Or
- Plus
- Addition
- Pred
- Saturating Decrement
- Times
- Multiplication