Is a class with only static methods preferable to a namespace?

Question

I was inspired by the comments under this question.

I didn't see any reason why a class with only static functions would be a better design than a namespace (with just functions). Any list of pros and cons of these two approaches are welcomed. It would be great with some practical examples!

A class with only static member functions would be familiar to Java programmers, and would encourage them to write C++ code as if it was Java. — Pete Becker, Apr 19 '13 at 15:58
@PeteBecker what if I only make friends with C++ developers? Lol — GuLearn, Apr 19 '13 at 15:59
@DanielFrey it is only a pro if you really really like the sight of `new`. — juanchopanza, Apr 19 '13 at 16:01
@AdriC.S. Yes, some people prefer that. Their preferences don't make it better or worse than the alternative, though. — Mike Seymour, Apr 19 '13 at 16:04
@GuLearn: Would you mind if I included static data members in this question, to generalize it a bit? — einpoklum, Aug 25 '17 at 20:29

R. Martinho Fernandes · Accepted Answer · 2013-04-19T16:09:27.867

11

One non-stylistic difference is that you can use a class as a template parameter, but you cannot use a namespace. This is sometimes used for policy classes, like std::char_traits.

Outside of that use case, I would stick to a namespace with regular functions.

edited Apr 19 '13 at 16:09

answered Apr 19 '13 at 16:02

R. Martinho Fernandes

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Throw in access specifiers as a difference, perhaps? – Drew Dormann Apr 19 '13 at 16:03
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@Drew what for? In a class with only static methods, there is nothing to encapsulate, by definition. – R. Martinho Fernandes Apr 19 '13 at 16:05
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public static methods implemented in terms of private ones that shouldn't be accessed directly. – Drew Dormann Apr 19 '13 at 16:07
@DrewDormann you can define whose *private* static methods in the .cpp file without declaring them in .h file in the namespace approach – GuLearn Apr 19 '13 at 16:14
@user2207811 In the (likely) case that any function is needed in only one translation unit, yes. – Drew Dormann Apr 19 '13 at 16:20

milleniumbug · Answer 2 · 2013-04-19T16:21:35.057

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Classes with static methods

You can have class inside another class, you can't have namespace inside class (because it probably does not make any sense).
They work with very ancient compilers.

Namespaces

~~- you can create namespace aliases~~

namespace io = boost::iostreams; Well, you can typedef classes, so this is moot point.

you can import symbols to another namespaces.

namespace mystuff { using namespace boost; }
you can import selected symbols.

using std::string;
they can span over several files (very important advantage)
inline namespaces (C++11)

Bottom line: namespaces are way to go in C++.

edited Apr 19 '13 at 16:21

answered Apr 19 '13 at 16:05

milleniumbug

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Actually, namespace inside classes make a _lot_ of sense. – einpoklum Aug 25 '17 at 20:28
It would be good to explain why "they can span over several files" is an important advantage. – Mert Mertce Oct 17 '19 at 10:57

Is a class with only static methods preferable to a namespace?

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