Question

Possible Duplicate:
C# generic constraint for only integers

As you can see in the following code, I need to compute the sum of two generic numbers.

public class NumberContainer<T>
{
    public T ValueA { get; private set; }
    public T ValueB { get; private set; }
    public T Total { get { return ValueA + ValueB; } }
}

However, it isn’t possible to do a direct addition of the two T values, which results in the compiler error below :

Operator ‘+’ cannot be applied to operands of type ‘T’ and ‘T’

Given that I don’t intend to use T for anything else than value-types that represent numbers (short, ushort, int, uint, etc), how could I perform the sum? (efficiency is a factor to be considered)

Answer 1

You can do it with “little magic” from LINQ:

private static readonly Func<T, T, T> adder;
static NumberContainer() {
    var p1 = Expression.Parameter(typeof (T));
    var p2 = Expression.Parameter(typeof (T));
    adder = (Func<T, T, T>)Expression
        .Lambda(Expression.Add(p1, p2), p1, p2)
        .Compile();
} 
public T Total { get { return adder(ValueA, ValueB); } }

The only drawback is that this code will compile even if NumberContainer is instantiated with a type T that does not support addition; of course it will throw an exception at run-time. An added benefit is that this should work with user-defined + operators.