c++ autoconvert inherited class to base class - c++

Question

I have one problem on conversion of one class to base.
This is the code :
#define Derive_NTag_CRTP(Type) class Type: public NTagBase<Type>
template<typename Derived>
class NTagBase{
public:
NTagBase(var name) { this->_name = name; }
NTagBase(const NTagBase & ntag) { this->_name = ntag._name; }
NTagBase* append(NTagBase<Derived> *item) { _children.push_back(item); return this; }
private:
var _name;
vector<NTagBase *> _children;
};
Derive_NTag_CRTP(NTag){
public:
NTag(var name) : NTagBase(name) { }
NTag(const NTagBase & ntag) : NTagBase(ntag) { }
};
Derive_NTag_CRTP(NTagInput){
public:
NTagInput(var type) : NTagBase("input") { _type = type; }
NTagInput(const NTagBase & ntag) : NTagBase(ntag) { }
private:
var _type;
};
int main(int argc, char **argv, char **envv)
{
NTag div("div");
NTagInput button("button");
div.append(new NTag("span"));
div.append(&button);// Error 1 error C2664: 'NTagBase<Derived>::append': can not convert parameter 1 from 'NTagInput *' to 'NTagBase<Derived> *'
}
How can I fix that without do one explicit cast?
PS: I need to have one vector of pointers of base class and append into that all kind of classes inherited.

Answer 1

div is NTag, i.e. NTagBase<NTag>. button is NTagInput, i.e. NTagBase<NTagInput>, while div's append() expects a NTagBase<NTag> which is unrelated. You should change append to something like
template <typename D>
NTagBase* append(NTagBase<D> item) { ... }
However, you still cannot store items of different types in a single vector. Better make a non-template e.g. Base of NTagBase and let your vector contain pointers (or std::unique_ptr) to Base.

Answer 2

div.append (...) clearly need to be overloaded because after inherited from the base, it wouldn't understand the second signature ie div.append(&button); or you can create a wrapper class that pack every object type to it own define and provide a mechanism for reversing back to the original type.
Alternatively , just overload any necessary function .
class NTagInput;
class AppendInputRegister;
template<typename Derived>
class NTagBase{
public:
NTagBase(string name) { this->_name = name; }
NTagBase(const NTagBase & ntag) { this->_name = ntag._name; }
NTagBase* append(NTagBase<Derived> *item) {
_children.push_back((NTagBase *)item);
return this;
}
private:
string _name;
vector<NTagBase *> _children;
};
class NTag: public NTagBase<NTag>{
public:
NTag(string name) : NTagBase(name) { }
NTag(const NTagBase & ntag) : NTagBase(ntag) { }
NTagBase* append(NTagBase<NTagInput> *item) {
append((NTagBase<NTag> *)item);
}
NTagBase* append(NTagBase<NTag> *item) {
NTagBase::append((NTagBase<NTag> *)item);
}
};
class NTagInput: public NTagBase<NTagInput>{
public:
NTagInput(string type) : NTagBase("input") { _type = type; }
NTagInput(const NTagBase & ntag) : NTagBase(ntag) { }
private:
string _type;
};