on Sun Oct 14 2012, "Jeffrey Lee Hellrung, Jr." <jeffrey.hellrung-AT-gmail.com> wrote:
On Sun, Oct 14, 2012 at 12:23 AM, Andrzej Krzemienski <akrzemi1@gmail.com>wrote: [...]
Can you help me understand one thing about pseudo-signatures? If I have the following concept:
concept MyIter<typename It> { It& operator++(It&); bool It::is_valid(); }
Does this say preincrement returns exactly reference to It or only something convertible to It? If it is the latter, it would mean that the concept model where pre-increment only returns something convertible to It& satisfies the concept, but makes the following usage invalid:
template <MyIter It> void test_next(It i) { return (++it).is_valid(); }
Or am I wrong?
My understanding, based only on reading this thread, is that, since It is declared as a model of MyIter (I'm not sure what the correct terminology is to express the relationship between It and MyIter within the scope of a "template <MyIter It>" declaration, but that's what I mean by "is declared as a model of"), ++it in the above context refers to the (pseudo-?)signature declared in the MyIter concept definition (hence has return type It&).
Precisely.
The operator++ within the MyIter concept definition implicitly (by default?) uses the operator++ of It, plus it adds a (implicit) conversion of the result to an It&, if necessary.
Precisely again.
So I would think the body of test_next would be entirely valid (no pun intended)...modulo the attempted bool -> void conversion :)
:-)
Aside: This discussion, of which I've only been a casual observer, has definitely been interesting.
Glad to help. -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost