Re: [boost] [bind] Placeholders suggestion, std and boost

Subject: Re: [boost] [bind] Placeholders suggestion, std and boost
From: Peter Dimov (lists_at_[hidden])
Date: 2015-05-25 14:02:05

Glen Fernandes wrote:
> On Mon, May 25, 2015 at 4:12 AM, Peter Dimov wrote:
> > Glen Fernandes wrote:
> >>
> >>   #include <boost/bind/bind.hpp>
> >>
> >>   using boost::placeholders::_1;
> >
> > I'm having a bit of trouble deciding between the above and
> >
> >    using namespace boost::placeholders;
> >
> > The using declarations are closer to the current code and would be a 
> > better bet compatibility-wise, but the using directive seems more 
> > correct somehow.
>
> With the former, ::boost::placeholders::detail (if it exists now, or will 
> in the future) would not become ::detail, if that matters.

There'll be nothing in boost::placeholders except _1.._9. Not 100% sure 
about the future.

The using directive allows you to declare your own _1 in the global 
namespace:

#include <boost/bind.hpp>

int _1;

int main()
{
    ::_1 = 5;
}

This works now. It's possible to make it work with the using declarations as 
well, if we put them into an unnamed namespace. But the idiomatic way to use 
the standard placeholders is "using namespace std::placeholders;", so I tend 
towards the same.