Re: [boost] Performance comparison between ptr_vectorandvector<cow_ptr<Shape> >, vector<copy_ptr<Shape> >
"Thorsten Ottosen" <tottosen@dezide.com> wrote in message news:<dpm9i3$4q4$1@sea.gmane.org>...
David Maisonave wrote:
"Sam Partington" <sam.partington@gmail.com> wrote in message news:<546fdb840601060205w76ed8be9n2bf73c4323c78c20@mail.gmail.com>.. .
I don't agree with that. The clone concept is a well established idiom for polymorphic types. Sure missing out a clone _does_ lead to slicing, but that is understood, and as Thorsten says we can help check for that with an assert. We can only help the user to get it
write, we can't do it all for them.
The cow_ptr and the copy_ptr can use the same assert code to catch slicing. The assert logic can be placed in the constructor of the cow_ptr and copy_ptr. This would make it easier to catch slicing in the cow_ptr/copw_ptr *than* it would be in the boost pointer containers. That's because in the boost pointer containers you would only catch slicing via assert if and when the object is clone. If the object never gets clone during testing, you would never catch the slicing.
With cow_ptr/copy_ptr the slicing would be caught when the object gets instantiated. So you have a much higher probability of catching
slicing using the cow_ptr clone method, *than* you would using the boost pointer container method.
I'm not sure I fully understand how the detection mechanism would work in your cow_ptr.
Example code: template<typename T_obj> cow_ptr(T_obj* type): m_ref_count(new ref_count(type, get_alloc_func(type))) { assert(typeid(*type) == typeid(T_obj)); } Since the cow_ptr works by capturing the type on the constructor, it can easily determine if the right type is being passed in, and if it matches the pointee type. That can't be done with the boost pointer containers because they don't catch the type on the constructor, nor is it part of the required logic for using a clone function method.
Nevertheless, as soon as the object is outside a cow_ptr might be sliced. That's reason enough not to allow it.
I'm not sure what you're referring to here. Can you post an example?
David Maisonave wrote:
"Thorsten Ottosen" <tottosen@dezide.com> wrote in message
I'm not sure I fully understand how the detection mechanism would work in your cow_ptr.
Example code: template<typename T_obj> cow_ptr(T_obj* type): m_ref_count(new ref_count(type, get_alloc_func(type))) { assert(typeid(*type) == typeid(T_obj)); }
how can that assertion ever fail when T_obj is deduced?
Since the cow_ptr works by capturing the type on the constructor, it can easily determine if the right type is being passed in, and if it matches the pointee type. That can't be done with the boost pointer containers because they don't catch the type on the constructor, nor is it part of the required logic for using a clone function method.
Nevertheless, as soon as the object is outside a cow_ptr might be sliced. That's reason enough not to allow it.
I'm not sure what you're referring to here. Can you post an example?
*ptr = *ptr2; -Thorsten
participants (9)
-
David Maisonave -
Thorsten Ottosen