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

Subject: Re: [boost] [proto] Problems with operator <<
From: John Maddock (boost.regex_at_[hidden])
Date: 2011-08-25 11:57:53

>> 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.
>
> Why answer you own question when I answered it for you yesterday?
>
> http://article.gmane.org/gmane.comp.lib.boost.devel/222816

Strange... that was exactly the answer I needed but it didn't show up in my 
inbox... would have saved me some time too :-(

> And I think you have a reason to actual disable proto's operators
> instead of just hide them. Check the msg I sent yesterday.

The thing is I need left and right shift to be protoized, but I also need to 
be able to overload for stream out, I ended up with several overloads 
looking like:

template <class Stream, class Backend>
typename enable_if<is_convertible<Stream*, std::ostream*>, 
std::ostream&>::type operator << (Stream& os, big_number<Backend>& r)

Which did the trick, and preserve protos shift operators, while still 
working with all stream types.

BTW I do specify a proto grammar, and only enable the operators I need on a 
case by case basis, in this case though I would need to restrict the grammar 
so that proto's shift operators are only enabled for RHS arguments of 
integer type.   Is that possible?

John.