Kristopher Johnson Kristopher Johnson - 3 months ago 10
C++ Question

Use 'class' or 'typename' for template parameters?


Possible Duplicate:

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."


  • They are equivalent (except as noted below).

  • Some people have reasons to always use
    typename
    .

  • Some people have reasons to always use
    class
    .

  • Some people have reasons to use both.

  • Some people don't care which one they use.



Note, however, in the case of template template parameters, use of
class
instead of
typename
is required. See user1428839's answer below. (But this particular case is not a matter of preference, it is a requirement of the language.)

Answer

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.

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