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    <p>The real value type of the iterator could well be the iterator itself. <code>operator*</code> may easily just return a reference to <code>*this</code> because the real work is done by the assignment operator. You may well find that <code>*it = x;</code> and <code>it = x;</code> have exactly the same effect with output iterators (I suppose special measures might be taken to prevent the latter from compiling).</p> <p>As such, defining the real value type would be just as useless. Defining it as a <code>void</code>, on the other hand, can prevent errors like:</p> <pre><code> typename Iter::value_type v = *it; //useless with an output iterator if it compiled </code></pre> <p>I suppose this is just the limit of the concept of output iterators: they are objects which "abuse" operator overloading, so as to <em>appear</em> pointerlike, whereas in reality something completely different is going on.</p> <p>Your problem is interesting, though. If you want to support any container, then the output iterators in question would probably be <code>std::insert_iterator</code>, <code>std::front_insert_iterator</code> and <code>std::back_insert_iterator</code>. In this case you could do something like the following:</p> <pre><code>#include &lt;iterator&gt; #include &lt;vector&gt; #include &lt;string&gt; #include &lt;map&gt; #include &lt;iostream&gt; //Iterator has value_type, use it template &lt;class T, class IterValue&gt; struct value_type { typedef IterValue type; }; //output iterator, use the container's value_type template &lt;class Container&gt; struct value_type&lt;Container, void&gt; { typedef typename Container::value_type type; }; template &lt;class T, class Out&gt; void parse_aux(Out out) { *out = typename value_type&lt;T, typename Out::value_type&gt;::type("a", "b"); } template &lt;template &lt;class&gt; class Out, class T&gt; void parse(Out&lt;T&gt; out) { parse_aux&lt;T&gt;(out); } //variadic template in C++0x could take care of this and other overloads that might be needed template &lt;template &lt;class, class&gt; class Out, class T, class U&gt; void parse(Out&lt;T, U&gt; out) { parse_aux&lt;T&gt;(out); } int main() { std::vector&lt;std::pair&lt;std::string, std::string&gt; &gt; vec; parse(std::back_inserter(vec)); std::cout &lt;&lt; vec[0].first &lt;&lt; ' ' &lt;&lt; vec[0].second &lt;&lt; '\n'; std::map&lt;std::string, std::string&gt; map; parse(std::inserter(map, map.end())); std::cout &lt;&lt; map["a"] &lt;&lt; '\n'; //just might also support normal iterators std::vector&lt;std::pair&lt;std::string, std::string&gt; &gt; vec2(1); parse(vec2.begin()); std::cout &lt;&lt; vec2[0].first &lt;&lt; ' ' &lt;&lt; vec2[0].second &lt;&lt; '\n'; } </code></pre> <p>It would still only get you this far. I suppose one could take this further, so it can also manage, say, a <code>std::ostream_iterator&lt;printable_type&gt;</code>, but at some point it would get so complex that it takes a god to decipher the error messages, should something go wrong.</p>
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