Re: [boost] possible addition to operators library

From: David Abrahams (dave_at_[hidden])
Date: 2003-02-25 08:00:19

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

> Hi,
>
> While making myself an interim shared_resource class, I found myself reusing
> the shared_ptr safe-bool conversion, and thought that really the idiom ought
> to go into the operators library.
>
> I am unsure about the name, but for now bool_testable seems to match the
> naming style used by the rest of operators, and be reasonably clear about
> its intent.  Any suggestions gratefully received
>
> Essentially you supply a operator! and it supplies an unspecified-bool-type
> conversion operator.
>
>
>  //Key
>  //T: primary operand type
>  //t: values of type T
>
>
>  // Template    Supplied Operations     Requirements
>  //
>  // bool_testable<T>  operator unspecified-bool-type() !t
>
>  template <class T, class B = ::boost::detail::empty_base> struct
> bool_testable : B
>  {
>  private:
>   void safe_bool_conversion() const { }
>  public:
>
>   typedef void (bool_testable<T, B>::*unspecified_bool_type)() const;
>   operator unspecified_bool_type() const
>   {
>    return !static_cast<const T&>(*this) ? 0 : &bool_testable<T,
> B>::safe_bool_conversion;
>   }
>  };
>
> Any problems with this?

None that I can see.

If you want to submit it, make a patch that includes changes to the
tests and the documentation, and post it here *as an attachment* so
that line-wrapping doesn't wreck it ;-)

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