C++ Methods – Member Functions vs. Non-Member Functions for Math Operators

clibrariesmethods

I'm writing a linear algebra library (long story short, it's a school assignment) that involves matrices, vectors, etc. In the process of creating this library, I'm going to be creating functions that perform mathematical operations on objects. For example, transpose matrix, invert matrix, normalize vector, etc.

I was curious as to what is the "best practice" for this sort of function… That is, should I make the function a member function, or non-member? (For clarity/library use sake)

Example:

//Member function way:
B = A.transpose();
C = A.inverse();

//Non-member function way:
B = linalg::transpose(A); //Non-member transpose function in linear algebra namespace
C = linalg::inverse(A);

Is there some standard regarding these sorts of operations? Or, at least, is there a common way people do this? I'm leaning towards the first option, but I'd like to know if this is recommended.

Best Answer

This is just a matter of style and taste. I have seen different linear algebra libraries, either

written in an OOP style using member functions
written in a non-OOP style using only free functions
providing an API with both

and all of them were working. At least, your API should be consistent, so pick your choice and make sure you don't mix those styles arbitrarily.

Related Solutions

C++ – Calling Non-Member Functions with Member Syntax

re your #2: Actually, making functions non-members often increases encapsulation, as Scott Meyers observed more than a decade ago.

Anyway, what you describe sounds much like C#'s extension methods to me. They are good to soothe the minds of those that are frightened when they see totally free functions. :) Once you've braved the STL (which, BTW, is not the standard library, but only that part of it which comes from the original STL) where almost all functions are so free that they aren't even real functions, but function templates, you will no longer need those.

In short: Don't try to bend a language to adapt to your mindset. Instead enhance your mindset to embrace the language's philosophy. You will emerge a bit taller from doing so.

C++ Design – Why C++ Complex Functions Are Not Member Functions

Am I missing something about how the standard library is designed which justifies why these functions are free?

The C++ standard library does not exclusively follow the OO design paradigm.

Free functions, when combined with parameter overloading, play much nicer when you are writing templated code that should work with both class types and primitive types.

For example, suppose I have a list of values (either complex, as std::complex<float>, or real, as float) and I want to compare them on magnitude. Then I can write a comparison function like

template <class T>
bool magnitude_less(const T& lhs, const T& rhs)
{
  using std::abs;
  return abs(lhs) < abs(rhs);
}

Writing such a function would not be possible if abs for std::complex<T> would have been a member function based on OO design principles.

Best Answer

Related Solutions

C++ – Calling Non-Member Functions with Member Syntax

C++ Design – Why C++ Complex Functions Are Not Member Functions

Related Topic