Re: [boost] [proto] Problems with operator <<

Subject: Re: [boost] [proto] Problems with operator <<
From: John Maddock (boost.regex_at_[hidden])
Date: 2011-08-25 04:08:47

> Folks,
>
> I'm having no end of problems with operator<< and proto.
>
> In the beginning, operator << was overloaded for stream output and 
> everything worked OK, then I added the left shift operator<< to the list 
> of protoized operators in the grammar and everything broke.  The strange 
> thing is that:
>
> std::cout << a+b;
>
> correctly finds my stream out overload:
>
> template <class Exp>
> inline std::ostream& operator << (std::ostream& os, const 
> big_number_exp<Exp>& r)
>
> But
>
> std::cout << a;
>
> no longer calls:
>
> template <class Backend>
> inline std::ostream& operator << (std::ostream& os, const 
> big_number<Backend>& r)
>
> But calls the proto << operator instead.
>
> I'm at a complete loss to explain this, both of my overloads are in the 
> same namespace as their respective types, and as far as I can see both 
> should be preferred to the proto versions.

To answer my own question - in case anyone else gets bitten by this - the 
answer is you need to provide overloads with both const and non-const 
reference RHS arguments to effectively hide the proto operator versions.

Still some hair left yours.... John.