Arithmetic Operators vs Methods in Class Design Guidelines

Question

I have many math types like Point3, and I am running into the dilemma of implementing operators, instance and static methods for arithmetic.

So say the type is Point3. Where a, b, c is a Point3, I sure wanna be able to say:

c = a + b;

But should I also implement:

c = Point3.Add (a, b);

And this:

c = a.Add (b);

To me #3 is useless and less readable than #1. And #2 seems like pointless unless you have an interface for Add, Subtract, Multiply, Divide, etc.

What do you recommend? Is there any problem or drawback with just having the operators (+, -, *, /)? Would this impede the generics arithmetic (I know it doesn't support it directly, but maybe having static methods would be useful in a workaround)?

Would a guidelines for this matter whether it's a class or a struct?

EDIT: Also for #3, I forgot to mention that this is for an immutable type, so returns a new Point3, instead of changing a.

Answer 1

In general, I think Microsoft seems to have kind of done A+B in most of their classes similar to this.

For samples, see the entire System.Windows.Media.Media3D namespace, as well as the XNA math classes. Both have point/vector/quaternion/matrices/etc, and use Class.Operator(a,b), and occasionally do c = a + b;

Personally, I would do the first where it makes sense and is clear, and always do the second option. I usually implement the first using the second option (the operator is implemented using the static method).

Answer 2

Use operator overloads to meet your needs. To honor .NET languages that do not support overloaded operators, include static methods that wrap the operators (or the other way around). The third option is only viable if you are using reference types and want to avoid instantiating new ones.

Answer 3

Languages, such as VB.NET, don't have operator overloading like C# does so they need static methods like your Point3.Add(a, b) to provide addition and other arithmetic operations. If you want your type to be CLR-compliant, you have to support these other languages by providing these method implementations.

Although VB.NET (and other language) programmers could use the op_Addition call created when the + overload is compiled, it is nicer to access an Add method. This MSDN section describes the alternative method names for each operator.

The third option you describe is not required for CLS-compliance.