Hi, I recently came across a request to make iterator_range<I>::size() SFINAE-friendly [1]. The respect in which it is not currently SFINAE-friendly is that it is only applicable to instantiations where I is a random-access iterator, but it is defined for all instantiations, and fails with a static assertion if I is not random-access. This makes it impossible to use SFINAE techniques to detect whether "r.size()" is valid where r is some iterator_range. The suggested workaround is to give iterator_range a base class, specialize this base class for random-access iterators, and only define size() in this specialization. I think this deficiency and workaround can be generalized to any template class 'C<T>' with a member function 'foo' that is only applicable for a subset of valid template arguments for 'T'. I am curious what the Boost community thinks about applying this workaround (factoring out the member function into a base class) as a general rule in such situations? Is making the member function SFINAE-friendly worth the decrease in readability? Are there other disadvantages to this workaround? Are there alternative ways of making such a function SFINAE- friendly that don't require introducing a base class? Finally, if the consensus is that such a workaround is not justified in general, is there any reason it should be justified specifically for iterator_range<I>::size()? Regards, Nate [1] https://svn.boost.org/trac/boost/ticket/8011