Boost C++ Libraries: Ticket #3438: node algorithms not usable with custom pointer types

attachment set

anonymous — Sat, 12 Sep 2009 05:13:54 GMT

attachment → intrusive.patch

patch. replaces every instance of node_ptr(0) with node_ptr()

anonymous — Sat, 12 Sep 2009 05:17:06 GMT

my patch somehow wasn't created recursively, so files in intrusive/detail/* aren't included. please change those files manually.

Ion Gaztañaga — Sat, 12 Sep 2009 08:38:10 GMT

Why shouldn't be constructible from 0? A smart pointer that wants to be like a raw pointer should support 0 initialization.

anonymous — Sat, 12 Sep 2009 17:07:34 GMT

why should it be constructible from 0? I know that the intrusive containers are only supposed to support certain types of pointers as their VoidPointer, but the algorithms don't have that restriction. not all pointer types want to be like raw pointers and are constructible from raw pointers. in fact, shared_ptr is not constructible from 0. (just an example, I'm not trying to use shared_ptrs). it does accept raw pointers, but not 0, as a template<class Y> shared_ptr(Y *) is not instantiated for 0.

and the node algorithms can go far beyond using pointers. e.g. you could use file offsets as pointer types, with 0 being a valid offset, to build a tree that resides in a file. and it's a very easy fix with no downsides.

anonymous — Sat, 12 Sep 2009 22:47:34 GMT

unfortunately, there are more (and bigger) problems like that: e.g. tree_algorithms.hpp:143:

static node_ptr uncast(const_node_ptr ptr) {

return node_ptr(const_cast<node*>(::boost::intrusive::detail::get_pointer(ptr)));

}

why do you even have to typedef node_ptr in the node traits, when it's later assumed that node_ptr is castable to (node *)? I've seen that you offer the possibility of an ADL overload, but unfortunately that's still a dealbreaker. I can't convert my pointer type to a raw pointer.

can you explain to me what's the rational behind accepting const_node_ptr's in the tree_algorithms interface and then const-casting it all the time?

circular_list_algorithms doesn't have these problems, my linked list using the same pointer type works just fine.

status changed; resolution set

Ion Gaztañaga — Thu, 26 Aug 2010 11:24:09 GMT

status new → closed
resolution → wontfix

This feature request won't be supported since it requires massive reworking.