-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Friday 10 July 2009, Peter Dimov wrote:
Frank Mori Hess wrote:
And also I imagine generalized_shared could be implemented by copying the entire shared_ptr codebase and then making only minor changes.
shared_count can already take an arbitrary P/D pair, so you only need to copy shared_ptr itself, not the rest of the codebase.
Ah, ok. Based on your encouragement (at least in the relative sense, since everyone else's response has been negative :), I've implemented a first pass at generic_shared. For those just tuning in generic_shared is like a shared_ptr but can accept a more generic type as the "pointer". It can accept either a plain old pointer as its template type, or a class which: 1) has operator->() and operator*() 2) either has value_type/reference/pointer member typedefs, or a specialization of boost::smart_pointer_traits 3) has a is_null_pointer() free function findable by ADL 4) supports (in)equality comparison generic_shared can also be used by another smart pointer class with similar requirements, since it fulfills them all itself. So you could have monitor<generic_shared<T*> > , to bring back the monitor example. The code is in the file generic_shared.hpp (a fork of shared_ptr.hpp from trunk) which is located in the sandbox directory: https://svn.boost.org/trac/boost/browser/sandbox/fmhess/boost/smart_ptr The file can be copied into the main boost tree (I've been testing it with trunk). There is also a shared_ptr.hpp in the same directory, which implements shared_ptr on top of generic_shared. I used that mainly so I could do some testing of generic_shared using the shared_ptr tests unmodified. The tests pass, except for those which use enabled_shared_from_this or weak_ptr. Beyond that, I've played around a little with a few basic tests that use a user-defined pointer type, and also use a list iterator as the pointer type (with a deleter that uses the iterator to erase the element from its list). So, the current status is: no generic_weak (analogous to weak_ptr) yet, and no shared_from_this support. Also, there is an unresolved issue with respect to casting for non-plain old pointer types. generic_shared tries to apply boost::static/const/dynamic_pointer_cast to its pointer type, but ADL doesn't work for boost::static/const/dynamic_pointer_cast, and specialization won't work either. It seems I'll need to add a ADL hook for casts as suggested at the end of this thread: http://lists.boost.org/Archives/boost/2006/06/106406.php so user-defined pointer types can be support casting. So, before I spend any more time on it, is this something worth pursuing further as far as boost goes? Does it stand any chance of making it into the smart_ptr library? Is there a silent majority out there who thinks this is a worthwhile idea, or is it just me? I might even settle for a vocal minority :) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkpc0TMACgkQ5vihyNWuA4VC6ACfW9UfTkCHTbmPc8a+VH2oFU/c XDEAn2B8wckssSMUL9yK1XUqZPfCyl1r =u9n9 -----END PGP SIGNATURE-----