Re: [Boost-users] Meaning of or_<> with empty arguments

14 Dec 2008

      Mickael Wolff  writes:
...
Reetesh Mukul a écrit :
...
Hi,
This code compiles:-
If you don't have, get a book about C++ ;) . Templates can have 
default parameters like functions :
template<typename LEFT = bool, typename RIGHT = bool>
compare(LEFT, RIGHT) ;
;) This I know. I meant something very different. 

I wanted to ask what can be the meaning of "or" operation on an empty
list/vector of parameters. Here or_<> is provided an empty set of parameters. 

Now looking into code of or_<> it appears that for no-parameters, it will
inherit from false_. But when I have compiled code ( in my last mail ) using gcc
(4.1), I saw that there were no "type" inside or_<>. Typically or_ has
a type in it.

Strange enough, but reasonable, or_ has a type inside it ( the false_
one ).

Now if suppose or_<> to false, how one is going to evaluate

typedef and_ > tto;

So please clear my gcc observation and the mathematical context of or_<>.

With Regards,
Reetesh Mukul