Question

I have two or more variables of class object in c# which has integer values. i want to overload ‘+’ operator so that i won’t have to convert these variables when ever i want to add or subtract them. here is my code below:

public static object operator +( object obj1, object obj2)
{
    object o = Convert.toint32(obj1) + Convert.toint32(obj2);
   return o;
}

no the problem is i am getting an error saying "One of the parameters of a binary operator must be the containing type"

why is this happening? any help is appreciated!

Answer 1

The compiler error tells you exactly what’s wrong – if you’re going to create a custom binary operator, at least one of the parameter types (for the operands) has to be the same as the type you’re declaring the operator in (or a nullable version of it, for value types).

This is mandated in section 10.10.2 of the C# 4 specification:

The following rules apply to binary operator declarations, where T denotes the instance type of the class or struct that contains the operator declaration:

• A binary non-shift operator must take two parameters, at least one of which must have type T or T?, and can return any type.
• A binary << or >> operator must take two parameters, the first of which must have type T or T? and the second of which must have type int or int?, and can return any type.

Personally I would try to avoid having variables of type object if you know they’re actually int values. Why not have int variables instead?

If you’re using C# 4, another alternative would be to make them dynamic variables, where the operator overloading would be applied at execution time rather than compile time.