C++ difference of keywords ‘typename’ and ‘class’ in templates
When defining a function template or class template in C++, one can write this:
template <class T> ...
or one can write this:
template <typename T> ...
Is there a good reason to prefer one over the other?
I accepted the most popular (and interesting) answer, but the real answer seems to be "No, there is no good reason to prefer one over the other."
Note, however, that before C++17 in the case of template template parameters, use of
class instead of
typename was required. See user1428839's answer below. (But this particular case is not a matter of preference, it was a requirement of the language.)
Stan Lippman talked about this here. I thought it was interesting.
Summary: Stroustrup originally used
class to specify types in templates to avoid introducing a new keyword. Some in the committee worried that this overloading of the keyword led to confusion. Later, the committee introduced a new keyword
typename to resolve syntactic ambiguity, and decided to let it also be used to specify template types to reduce confusion, but for backward compatibility,
class kept its overloaded meaning.
According to Scott Myers, Effective C++ (3rd ed.) item 42 (which must, of course, be the ultimate answer) - the difference is "nothing".
Advice is to use "class" if it is expected T will always be a class, with "typename" if other types (int, char* whatever) may be expected. Consider it a usage hint.