[Boost-users] [Bind] Placeholders passed by reference?

This works exactly as expected... void f( unsigned & val ) { val *= 2; } unsigned i = 3; boost::bind( f, _1)( i ); with i being doubled. What I don't get is why I don't need to say boost::bind( f, boost::ref( _1 ) )( i ); and conversely how I specify that I want bind to pass by value rather than by reference for the placeholder. Thanks - Rob.