see this question: Effective C++ Item 23 Prefer non-member non-friend functions to member functions and also C++ Member Functions vs Free Functions You should prefer free functions, in the extent that it promotes loose coupling. Consider making it a member function only if it works on the guts of your class, and that you consider … Read more
If the function is only used in one source file, it makes perfect sense to define it there. If nobody else is using it, it doesn’t belong in the header. As you say, it reduces dependencies and can potentially save some recompiles.
In the semi large projects where I usually work (more than 2 million lines of code) I would ban private class functions if I could. The reason being that a private class function is private but yet it’s visible in the header file. This means if I change the signature (or the comment) in anyway … Read more
The only situation in which a nameless namespace in header can be useful is when you want to distribute code as header files only. For example, a large standalone subset of Boost is purely headers. The token ignore for tuples, mentioned in another answer is one example, the _1, _2 etc. bind placeholders are others.
You’re basically referring to the section ยง7.3.1.1/2 from the C++03 Standard, The use of the static keyword is deprecated when declaring objects in a namespace scope; the unnamed-namespace provides a superior alternative. Note that this paragraph was already removed in C++11. static functions are per standard no longer deprecated! Nonetheless, unnamed namespace‘s are superior to … Read more
The C++ Standard reads in section 7.3.1.1 Unnamed namespaces, paragraph 2: The use of the static keyword is deprecated when declaring objects in a namespace scope, the unnamed-namespace provides a superior alternative. Static only applies to names of objects, functions, and anonymous unions, not to type declarations. Edit: The decision to deprecate this use of … Read more
Unnamed namespace could be considered as a normal namespace with unique name which you do not know. According to C++ Standard 7.3.1.1: An unnamed-namespace-definition behaves as if it were replaced by namespace unique { /* empty body */ } using namespace unique; namespace unique { namespace-body } where all occurrences of unique in a translation … Read more