Why operator () [] -> = must be non-static member?
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  <p><strong>Possible Duplicate:</strong><br>
  <a href="http://stackoverflow.com/questions/1132600/why-are-some-operators-in-c-only-allowed-to-be-overloaded-as-member-functions">Why are some operators in C++ only allowed to be overloaded as member functions?</a>  </p>
</blockquote>



<p>Why operator () [] -> = must be non-static member? Why it can't be friend?</p>
