Are members of a class template instantiated when the class is instantiated?

Question

Supposedly members of a template class shouldn't be instantiated unless they are used. However this sample seems to instantiate the do_something member and the enable_if fails (which would be expected if we'd instantiated it - but AFAIK we did not).

Am I missing something really basic here?

#include <string>
#include <boost/utility.hpp>

struct some_policy {
    typedef boost::integral_constant<bool, false> condition;
};

struct other_policy {
    typedef boost::integral_constant<bool, true> condition;
};


template <typename policy>
class test {
   void do_something(typename boost::enable_if<typename policy::condition>::type* = 0) {}
};

int main() {
    test<other_policy> p1;
    test<some_policy>  p2;
}

coliru

Answer 1

From C++11 14.7.1/1:

The implicit instantiation of a class template specialization causes the implicit instantiation of the declarations, but not of the definitions or default arguments, of the class member functions

So the function declaration is instantiated; that fails since it depends on an invalid type.

_{(Unfortunately, I don't have any historic versions of the standard to hand, but I imagine this rule was similar in C++98)}