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For example uninitialized_copy is defined in the standard as: Effects: for (; first != last; ++result, ++first) ::new (static_cast<void*>(&*result)) typename iterator_traits<ForwardIterator>::value_type(*first); If understood literally, this is a requirement to call operator ,(ForwardIterator, InputIterator) . And in fact this code prints Hello world! ten times: #include <memory> #include <iterator> #include <iostream> using namespace std; namespace N { struct X : iterator<forward_iterator_tag, int> { pointer _p; X(pointer p) : _p(p) {} X& operator++() { ++_p; return *this; } X operator++(int) { X r(*this); ++_p; return r; } reference operator*() const { return *_p; } pointer operator->() const { return _p; } }; bool operator==(X a, X b) { return a._p == b._p; } bool operator!=(X a, X b) { return !(a == b); } void operator,(X a, X b) { cout << "Hello world!\n"; } } int a[10], b[10]; int main() { using N::X; uninitialized_copy(X(a), X(a+10), X(b)); } However, for most other algorithms the standard gives the description in prose. E.g. for copy there's no requirement for operator , to be called. But if I change uninitialized_copy(X(a), X(a+10), X(b)); in the above code to copy(X(a), X(a+10), X(b)); then Hello world! is still printed ten times . The said results are observable in both, VS2005 and GCC 4.3.4. However, if I write mismatch(X(a), X(a+10), X(b)); instead, then VS2005 prints Hello world! ten times but GCC does not. Unfortunately I couldn't find where the standard prohibits <code

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