Re: using vector to encapulate a tree - non const copy constructors
news1@lyonstech.net (terry) wrote (abridged):
[...] it seems natural to first approach your remark that
it is out of fashion, or even dissaproved of to derive from containers.
I agree that there seems to be a predudice against this - but I think it
really is predudice - coming from a historic overinvolvement with
polymorphism. It seems to me that C++ becomes really powerful when one
combines derivation and templates. I find myself wanting to derive from
the map class all the time in my work.
Inheritance is a very tightly coupled relationship. One danger is that all
the names of the base class are injected into the derived class. Another
is that the base class can call any functions in the derived class, even
private ones, if it happens to declare a virtual function with the same
signature itself.
The upshot is that we generally avoid using inheritance where it is not
necessary, and it's not necessary here. Your example class could be
written with a vector member and forwarding functions instead. Eg:
template<typename T, typename Id>
class my_vector {
typedef std::vector<T> Base;
Base base;
public:
typedef Base::iterator iterator;
typedef Base::const_iterator const_iterator;
bool empty() const { return base.empty(); }
size_t size() const { return base.size(); }
// Scores more forwarding functions.
};
It's slightly more work, but since this template is generic we only need
to do it once so that isn't significant.
Incidently, I replaced the int parameter with a type so you don't have to
mess with allocating numbers to types. Instead of:
typedef my_vector<double,2> row_vector_double;
you'd have:
struct row_tag {};
typedef my_vector<double,row_tag> row_vector_double;
-- Dave Harris, Nottingham, UK.
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