disabling unary "-" for unsigned types

[Adam D. Ruppe]

On Tue, Feb 16, 2010 at 11:26:37AM -0600, Ellery Newcomer wrote:
> OT: has anyone written a wrapper for int/long/etc that throws exceptions 
> on overflow/underflow? Maybe such a thing should exist in the standard 
> library?

Something along these lines should work (pasted at bottom of message).

I'd like it a lot more if it could just be opBinary!(string)() -- the struct
would be tiny.

Suckily, assigning an it to it when declaring it doesn't work. I think there's
a way around this, but I don't know.

The opPow's are commented out since my dmd is too old, so I couldn't test it.


========

import std.stdio;

struct NoOverflow(T) {
	T _payload;
	alias _payload this;

	T opAdd(T a) {
		T tmp = _payload + a;
		asm { jo overflow; }
		return tmp;
		overflow:
			throw new Exception("Overflow");
	}

	T opSub(T a) {
		T tmp = _payload - a;
		asm { jo overflow; }
		return tmp;
		overflow:
			throw new Exception("Overflow");
	}

	T opMul(T a) {
		T tmp = _payload * a;
		asm { jo overflow; }
		return tmp;
		overflow:
			throw new Exception("Overflow");
	}

	T opDiv(T a) {
		T tmp = _payload / a;
		asm { jo overflow; }
		return tmp;
		overflow:
			throw new Exception("Overflow");
	}

	/+
	T opPow(T a) {
		T tmp = _payload ^^ a;
		asm { jo overflow; }
		return tmp;
		overflow:
			throw new Exception("Overflow");
	}
	+/

	T opAddAssign(T a) {
		_payload += a;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}

	T opSubAssign(T a) {
		_payload -= a;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}

	T opMulAssign(T a) {
		_payload *= a;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}

	T opDivAssign(T a) {
		_payload /= a;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}

	T opPowAssign(T a) {
		//_payload ^^= a;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}

	T opPostInc() {
		_payload++;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}

	T opPostDec() {
		_payload--;
		asm { jo overflow; }
		return this;
		overflow:
			throw new Exception("Overflow");
	}
}

void main() {
	alias NoOverflow!(int) oint;

	oint a;
	a = int.max;
	a--;
	writefln("%d", a);
	a++;
	writefln("%d", a);
	a++; // should throw
	writefln("%d", a);
}

=======


-- 
Adam D. Ruppe
http://arsdnet.net