axter wrote:
"Slawomir Lisznianski" <public@paramay.com> wrote in message news:<donook$li2$1@sea.gmane.org>...
Hello,
I've been using ptr_map lately and have a few questions regarding its interface.
Below is a signature of `insert' function as declared in ptr_map_adapter:
std::pair<iterator,bool> insert( key_type& k, value_type x );
Why is `k' a non-const reference?
it's a matter about exception-safety. see the FAQ.
To imply ownership transfer, couldn't `x' be of `std::auto_ptr<value_type>' type instead?
right. the next release will have overloads taking auto_ptr<T> as well as T*.
What happend to std::pair as an argument of insert? Was symmetry with std::map dropped for a reason here?
yes, exception-safety.
From my test, it doesn't seem as though ptr_map has consistent and reliable implementation.
Do you care to explain in detail what that means?
I recommend that boost replace the pointer containers with the following smart pointers: http://code.axter.com/copy_ptr.h http://code.axter.com/cow_ptr.h
Example usage: std::map<int, cow_ptr<foo> > MyPtrMap;
The above type gives you more functionality then the boost::ptr_map type, and of course, it's interface matches the std::map interface. Where as the boost::ptr_map type has the following problems: 1. Doesn't allow you to use an abstract pointer
Really?
2. Requires a non-constant argument for the insert function
Right, to give exception-safety.
3. Requires value semantics for the operator[] function
?
4. When assigning value via operator[] from one container to another, you get object splicing for derived types
So?
5. It doesn't seem to compile on VC++ 6.0, and when it compiles on VC++ 7.1 you get compiler warnings
Yes, vc7.1 warns about a lot of things, particular ADL. Turn it off.
If you use cow_ptr instead, you don't have the above problems.
There are similar problems in the boost::ptr_set class, which also can be replaced with cow_ptr or copy_ptr std::set<cow_ptr<foo> > MyPtrSet;
IMHO, the entire boost pointer container set of classes can be replace with either cow_ptr and/or copy_ptr, and the result would be a more reliable,
reliable in what way? Switching to a deep-copying smart pointer can have significant performance implications, particularly (but not only) with compilers without RTO, like vc6. -Thorsten