"Thorsten Ottosen" <tottosen@dezide.com> wrote in message news:<dpglgo$cb1$1@sea.gmane.org>...
axter wrote:
"Thorsten Ottosen" <tottosen@dezide.com> wrote in message news:<dpgi92$18k$1@sea.gmane.org>...
axter wrote:
The pointer-containers don't slica anything on their own. If you insist on not making your class hierarchy non-copyable, I can't help you.
I don't see that making a difference, but could you please post a small example class that is non-copyable, so that I can test it out.
struct Foo { private: Foo( const Foo& ); Foo& operator=( const Foo& ); };
or
#include <boost/utility.hpp>
struct Bar : boost::noncopyable { };
In addition, an explicit copy-constructor will prohibit slicing on compliant compilers.
No, it doesn't. That's what I thought you where talking about, but I wanted to make sure before possibly putting my foot in my mouth.
Both the above methods prevent slicing of concrete types. However, it does not prevent slicing in pointer idiom. See following example code using booost::ptr_vector, and non-copyable types that get slice, where BasesS1 uses the first non-copyable method, and BasesS2
uses the boost::noncopyable method. Both end up getting slice when the container gets copied.
class BasesS1 { public: virtual BasesS1* do_clone()const=0; virtual string WhoAmI()const=0; BasesS1(int i = 0):m_i(i){} private: BasesS1( const BasesS1& ); BasesS1& operator=( const BasesS1& ); protected: int m_i; };
class DerivedS1 : public BasesS1 { public: DerivedS1(int i = 0):BasesS1(i){} BasesS1* do_clone()const{return new DerivedS1();} string WhoAmI()const{return "DerivedS1";} };
class DerivedDerivedS1 : public DerivedS1 { public: DerivedDerivedS1(int i = 0):DerivedS1(i){} string WhoAmI()const{return "DerivedDerivedS1";} };
[snip]
int main(int, char**) { boost::ptr_vector<BasesS1> vBaseS1_cpy1; vBaseS1_cpy1.push_back(new DerivedDerivedS1(123)); boost::ptr_vector<BasesS1> vBaseS1_cpy2(vBaseS1_cpy1.begin(), vBaseS1_cpy1.end()); cout << vBaseS1_cpy2[0].WhoAmI() << endl;
Note that DerivedDerivedS1/S2 does not implement do_clone().
Yes. That's exactly the point I'm trying to make. Both the boost pointer containers and the cow_ptr/copy_ptr method can result in splicing via improper usage. Both methods can produce splicing via derive-derive type, and both methods can produce splicing via derive type of a non-abstract type. Furthermore, making the class non-copyable does not prevent the splicing in a pointer idiom.