comp-time-dispatch.rs

pub trait Handler: Sized {
	fn address(&mut self, state: &mut Machine, opcode: Opcode, position: usize) -> Control;
}

type OpFn<H> = fn(this: &mut H, state: &mut Machine, opcode: Opcode, position: usize) -> Control;

// We would like to write this, but Rust's const-eval is not good enough for that yet :(
// const fn mk_table<H: Handler>() -> [OpFn<H>; 256] { }

// So, we have to express this as type-level function (trait)
trait MkTable<H: Handler> {
	const TABLE: [OpFn<H>; 256];
}
struct OpTable<H: Handler>(PhantomData<H>);
impl<H: Handler> MkTable<H> for OpTable<H> {
	const TABLE: [OpFn<H>; 256] = {
		let mut res: [OpFn<H>; 256] = [|_, _, _, _| Control::Exit(ExitError::OutOfGas.into()); 256];

		// Built-in op-codes
		res[Opcode::STOP.as_usize()] = (|_, s, o, p| eval_stop(s, o, p)) as OpFn<H>;

		// Customizable op-codes
		res[Opcode::ADDRESS.as_usize()] = H::address;

		res
	};
}

#[inline]
pub fn eval_with<H: Handler>(
	h: &mut H,
	state: &mut Machine,
	opcode: Opcode,
	position: usize,
) -> Control {
	OpTable::<H>::TABLE[opcode.as_usize()](h, state, opcode, position)
}