[boost] [bind] function_equal with binds holding weak_ptr values

From: Sylvester-Bradley, Gareth (Gareth.Sylvester-Bradley_at_[hidden])
Date: 2008-07-17 07:48:13

(Apologies for not posting my previous question in plain-text.)

Bind can be used with weak_ptr values, but should function_equal work
with binds holding weak_ptrs?

Since weak_ptr doesn't have operator==, the following results in a
compiler error:

#include <boost/function_equal.hpp>
#include <boost/bind.hpp>
#include <boost/weak_ptr.hpp>

int h( boost::weak_ptr<void> wp ) { return wp.use_count(); }

template < typename F > bool self_equal( F f_ )
{
  return function_equal( f_, f_ );
}

int main( int argc, char * const argv[] )
{
  self_equal( boost::bind( h, _1 ) ); // OK
  self_equal( boost::bind( h, boost::weak_ptr<void>() ) ); // compiler
error
  return 0;
}

Would it be appropriate to use operator< equivalence?

I suspect the answer may be "it depends...", but I made the above
compile by adding the following:

namespace boost
{
  namespace _bi
  {
    template<class T> class value< weak_ptr<T> >
    {
    public:
      value(weak_ptr<T> const & t): t_(t) {}
      
      weak_ptr<T> & get() { return t_; }
      weak_ptr<T> const & get() const { return t_; }
      
      bool operator==(value const & rhs) const
      {
        return !(t_ < rhs.t_) && !(rhs.t_ < t_);
      }
      
    private:
      weak_ptr<T> t_;
    };
  }
}

Is that a good or bad idea?

Thanks,
Gareth

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