Peter Dimov wrote:
Eric Niebler wrote:
General design question here. This came up on the user's list, and it made me question something I believed to be true. When writing a proxy for, e.g., a std container, I see two options for handling const.
0) Const-ness depends on the const-ness of the object being proxied:
1) Const-ness depends on the proxy object itself:
<snip>
If the vector_proxy has an ordinary copy constructor, (0) is usually correct because (1) cannot be enforced.
vector_proxy const a = ...; vector_proxy b = a;
That's a good point, and very relevant to the BOOST_FOREACH discussion because BOOST_FOREACH must make a copy of the proxy.
(1) typically only makes sense for types that are intended to be class members and propagate the constness of the member function to the proxied (referred to) object for some reason.
Right, that would seem to be a legitimate use.
(1) can work for move-only types. I don't have experience with such proxies, so I can't tell. :-)
You mean when the proxy is move only? How does that solve the problem above? vector_proxy const a = ...; vector_proxy b = std::move(a); I've probably misunderstood. -- Eric Niebler Boost Consulting www.boost-consulting.com The Astoria Seminar ==> http://www.astoriaseminar.com