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    <p>When you write </p> <pre><code> os &lt;&lt; tuple_.get&lt;0&gt;(); </code></pre> <p>there is no function that matches both parameters. Instead the compiler has a choice to apply an implicit conversion on either parameter</p> <pre><code>std::ostream &lt;&lt; int </code></pre> <p>or</p> <pre><code>std::ostringstream &lt;&lt; MyTuple </code></pre> <p>The latter would happen with the <code>boost::tuple</code> constructor that can take any number of arguments up to number of tuple elements. (And with <code>float</code> it fails, because <code>float</code> is convertible to <code>int</code>.)</p> <p>When overloading stream operators, use the base class as the left hand side (<code>ostream</code> or even <code>basic_ostream&lt;CharT, Traits&gt;</code>.</p> <hr> <p><strong>Edit:</strong> You could disambiguate the call by casting the <strong>first</strong> argument.</p> <pre><code>ostringstream&amp; operator&lt;&lt;(ostringstream&amp; os_, Mytuple tuple_) { static_cast&lt;std::ostream&amp;&gt;(os_) &lt;&lt; tuple_.get&lt;0&gt;(); static_cast&lt;std::ostream&amp;&gt;(os_) &lt;&lt; tuple_.get&lt;1&gt;(); static_cast&lt;std::ostream&amp;&gt;(os_) &lt;&lt; tuple_.get&lt;2&gt;(); // Error because no matching operator. Fine. return os_; } </code></pre> <p>However, overloading the operator with <code>ostringstream</code> is still a bad idea, because it won't work with operator chaining.</p> <pre><code>MyTuple a, b; ostringstream ss; ss &lt;&lt; a &lt;&lt; ' ' &lt;&lt; b; </code></pre> <p>will invoke:</p> <p>1) <code>ostringstream&amp; operator&lt;&lt;(ostringstream&amp; os_, Mytuple tuple_)</code></p> <p>2) <code>ostream&amp; ostream::operator&lt;&lt;(char)</code></p> <p>3) <strong><code>ostream&amp; operator&lt;&lt;(ostream&amp;&amp;, boost::tuple&lt;int,float,Myclass&gt;</code></strong></p>
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    1. POHow to write a `<<` operator for boost::tuple?
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    1. COIt would be easier to disambiguate writing: `os.operator<<(tuple_.get<1>());`
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