Re: [boost] is_single_element?

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2002-05-17 05:45:28

Peter Dimov wrote:
> 
> From: "Daniel Frey" <daniel.frey_at_[hidden]>
> >
> > template< typename Container >
> > bool is_single_element( const Container& container )
> > {
> >    // Resolved at compile-time:
> >    if( ::boost::is_pointer< Container::iterator >::value )
> >      return !container.empty() &&
> >        boost::next( container.begin() ) == container.end();
> >    else
> >      return !container.empty() &&
> >        ++container.begin() == container.end();
> > }
> 
> template<class It> bool is_single_element(It first, It last)
> {
>     return first != last && ++first == last;
> }

How does this help to prevent unneccessary temporaries? You just moved
them to the parameter list, don't you?

template< class Iterator >
bool is_single_element( Iterator first, const Iterator& last )
{
   return first != last && ++first == last;
}

template< class Container >
bool is_single_element( const Container& container )
{
   return !container.empty() &&
     ++Container::const_iterator( container.begin() ) ==
container.end();
}

Now we have several version that should work anywhere, but what is the
best one considering efficiency?

Regards, Daniel

--
Daniel Frey
aixigo AG - financial training, research and technology
Schloß-Rahe-Straße 15, 52072 Aachen, Germany
fon: [phone], fax: [phone]
eMail: daniel.frey_at_[hidden], web: http://www.aixigo.de