Why there is no base type of Number in c#?

Question

Unlike in java why c# does not have a supertype of Number for Floats, Integers etc? Any reasoning behind avoiding Number in c#?

Answer 1

Because value types can't be inherited.

Answer 2

what would you need that for?

Answer 3

But very useful, if they had included it, would have been for all integral numeric types (int, short, long, uint, etc.) to have been defined to implement an empty interface named IIntegral, and all numeric types (Integral plus decimal, float, etc.), to have been defined to implement an empty interface named INumeric.

This would have allowed generics to have specified constraints based on these interfaces to restrict allowable types to the integral types, or to numeric types, which is currently a much more difficult problem.

Answer 4

It might have performance reasons - Numbers, being struct-types, are stack-allocated and fast but do not allow inheritance structures. Using them in an OO-way would require a very large amount of auto/unboxing and additionally big much performance reductions due to much more memory consumption and vtable lookups to solve the polymorphism.

Java has introduced object-oriented wrappers and ends up with different and incompatible implementations for one and the same thing with is even more strange.

A better possibility for providing fast abstractions for numbers would be the introduction of typeclasses/concepts like in Haskell or C++ where you could write:

sum :: (Num t) => [t] -> t

read as Sum takes a list of elements of type t - where t is a number type - and returns such a number. This mechanism could be optimized away at compile-time without any performance overhead. But neither .NET nor Java have such techniques.

Answer 5

You could create an extension to Object that returns a bool for you, like so (untested, may provide false positives, etc.) (catches decimals, floats, ints, using US style delimiter for decimal; modify regex to fit hex, etc etc.)

public static class Object
{
    static Regex r = new Regex(@"^\d*\.*\d$", RegexOptions.Compiled);
    public static bool IsNumber(this object obj)
    {
        return r.IsMatch(obj.ToString() && !(obj is string);
    }
}

Since ToString is part of Object, and everything is ultimately a child of object...

Granted, this won't provide type safety or generics or anything like that, but it will still let you do similar things with a little more work. You didn't specify what you wanted the base class for, whether you want accept any numeric type as an argument someplace, or you wanted generics. This may get you partway to wherever you were going though.

Usage:

public class thingThatHasNumericValue
{
    private object arbNumber;
    public object SomeArbitraryNumber
    {
        get { return arbNumber; }
        set
        {
            if (!arbNumber.IsNumber())
            {
                throw new InvalidOperationException("Must be a number");
            }
            arbNumber = value;
        }
    }
}

Answer 6

I don't know if true, but one explanation I heard was weight - in particular for the small frameworks (Compact Framework, Silverlight, Micro Framework); I'm not convinced by this...

Far more convincing is that by itself knowing it is a number doesn't provide much; for example, integer division works very differently to floating point, and operators aren't always as simple as you'd like (think DateTime + TimeSpan => DateTime, DateTime - DateTime => TimeSpan).

If it helps, MiscUtil offers generic operator support, allowing things like:

T x = ..., y = ...; // any T that has suitable operators
T sum = Operator.Add(x,y);

All very cleanly and efficiently. Note, however, that there is no compile-time validation (since there are no suitable generic constraints). But it works.