C# number promotion in expression

Question

I am creating a generic operator method that can dynamically compare two objects of any type. For example:

Object a = (int)5;
Object b = (long)7;
return a < b;

Now this obviously won't compile because object does not provide the less than operator. Casting the objects back to their respective types would obviously work.

However I do not know the types at runtime.

If I could use .NET 4 (which I can't) then I could cast the objects to dynamic and all would be fine. However since I cannot, I believe I'm left with codegen using expressions, or providing casts for every possible type and value!

So expressions!

If I were to create an expression, I would need to unbox the object to the correct type (easy) but then I would need to promote any numerical type to the largest of either operand. The rules for promotion are documented in the C# specification.

My question is, is there any prewritten promotion code either in the framework or not or, am I going about this the wrong way!

Thanks for the help.

Update

Thanks for the answers. I must admit I wasn't thinking of using IComparable because the method will be used for more than numbers (although I didn't explicitly mention that). Having said that, I could probably check whether or not both objects implement the interface and use it if they do.

You wrote all that on an iPhone? You have nimbler fingers than I. — Eric J., Apr 19 '12 at 19:07
Thanks! It was just on my mind. Oh and thanks to minitech who formatted for me! — , Apr 19 '12 at 21:44

score 3 · Accepted Answer · answered Apr 19 '12 at 19:08

Using generics, if you use where T : IComparable, you could use a compare method on the objects (values)

static bool IsLessThan<T>(T a, T b) where T : IComparable
{
  return a.CompareTo(b) < 0;
}

For two different types:

static bool IsLessThan<T, V>(T a, V b) where T : IComparable where V : IComparable
{
  return a.CompareTo(b) < 0;
}

NOTE value types int, long, etc -- already are IComparable, how cool is that? :)

score 0 · Answer 2 · answered Apr 19 '12 at 19:10

0

The best way would probably be to use generics (if you're not already) and constrain the generic type to those types that implement IComparable, then use its CompareTo method.

answered Apr 19 '12 at 19:10

Ry-

218,210
55
464
476

C# number promotion in expression

2 Answers2