Re: [boost] possible addition to operators library

From: David Abrahams (dave_at_[hidden])
Date: 2003-02-25 09:55:05

"Sam Partington" <Sam.Partington_at_[hidden]> writes:

> I thought of this too, but this limits the user to using a member based
> operator!.  So I couldn't do this :
>
> class A : public boost::bool_testable<A>
> {
> public:
>     int get();
> };
>
> bool operator!(const A& a)
> {
>     return a.get() == 0;
> }
>
> Of course I've never actually wanted to do that, so its maybe not a problem.
> After all the conversion operator itself has to be a member, so it probably
> isn't much of a restriction at all.

Ahem.  The operators library is *all about* defining free function
operators.  I don't think you should introduce a dependence on being
a member function.

> Then again, how much does the safe_bool_conversion function cost?

More than I'd like.  I'd prefer to use a single data member pointer,
since it's likely to be more efficient.

   struct safe_bool
   {
#ifndef BOOST_NO_MEMBER_TEMPLATE_FRIENDS
    private:
       template <class T, class B> friend class bool_testable;
#endif
       int x;
       typedef int safe_bool::*type;
   };

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com