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POShould the implementation guard itself against comma overloading?
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copied!<p>For example <code>uninitialized_copy</code> is defined in the standard as:</p> <blockquote> <p><em>Effects:</em></p> <pre><code>for (; first != last; ++result, ++first) ::new (static_cast<void*>(&*result)) typename iterator_traits<ForwardIterator>::value_type(*first); </code></pre> </blockquote> <p>If understood literally, this is a requirement to call <code>operator ,(ForwardIterator, InputIterator)</code>. And in fact this code prints <code>Hello world!</code> ten times:</p> <pre><code>#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)); } </code></pre> <p>However, for most other algorithms the standard gives the description in prose. E.g. for <code>copy</code> there's no requirement for operator <code>,</code> to be called. But if I change</p> <pre><code> uninitialized_copy(X(a), X(a+10), X(b)); </code></pre> <p>in the above code to</p> <pre><code> copy(X(a), X(a+10), X(b)); </code></pre> <p>then <code>Hello world!</code> is <em>still printed ten times</em>. The said results are observable in both, VS2005 and GCC 4.3.4. However, if I write</p> <pre><code> mismatch(X(a), X(a+10), X(b)); </code></pre> <p>instead, then VS2005 prints <code>Hello world!</code> ten times but GCC does not.</p> <p>Unfortunately I couldn't find where the standard prohibits <code>operator,</code> overloading for iterator types. On the contrary, it prohibits the implementations to do calls as above [global.functions]:</p> <blockquote> <p>Unless otherwise specified, global and non-member functions in the standard library shall not use functions from another namespace which are found through argument-dependent name lookup (3.4.2).</p> </blockquote> <p>So who of the four parties is wrong: MSVC, GCC, ISO or me? (Choose one)</p>

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