Constraints, generic variables and arithmetic operators

Question

I’d like to declare a generic class Simple where a method called Addition would take two generic variables and add them together using + operator. I thought I could accomplish this by giving class Simple the following constraint:

class Simple<T> where T: int
{
    public T Addition(T firstInt, T secondInt)
    {
        return firstInt + secondInt;
    }
}

I suspect error has something to do with generics only having the following five types of constraints - ClassName, class, struct,InterfaceName, new()? Thus, why don’t generics also support StructureName constraint type? That way we would be able to apply arithmetic operators on generic variables?!

thanx

score 4 · Accepted Answer · answered Feb 12 '10 at 18:24

A StructName constraint wouldn't make sense, since you cannot inherit from value types.

If you had something like class Simple<T> where T : int you could only instantiate Simple<T> with T = int, no type inherits from int or any other value type for that matter.

C# (the CLR) lacks what other languages know as type classes, one popular mechanism to handle operator overloading without hard-coded compiler mechanics (like in C#).

score 2 · Answer 2 · answered Feb 12 '10 at 18:18

There is no point in constraining a Generic type to a specific struct, since struct types cannot be inherited. This would be identical to writing:

class Simple
{
    public int Addition(int firstInt, int secondInt)
    {
        return firstInt + secondInt;
    }
}

Unfortunately, with support for an IArithmetic interface, generic types with mathematical operations are difficult to support. If you want to see one approach for generic-based mathmetical operators, look to the Generic Operators in MiscUtil.

score 1 · Answer 3 · answered Feb 12 '10 at 18:20

You constrain T to int. This is no sensible thing to do, as there is only one int type; so you could directly want to write int if you want int.

If you do not constrain T, you cannot use the + operator, since there is no + operator defined on object.

C# generics are not C++ templates.

Constraints, generic variables and arithmetic operators

3 Answers3