templates / Q_OBJECT question

[wysota]

I admit I haven't read the whole post, but it looks like templates are not for you - you can't decide which class to create during runtime, the template argument has to be specified during compilation. But if you think templates are for you, then make some object that is not derived from QObject and make it a member of your class - QObjects can't be templates, but they can have a member pointer that is a base class of a template class.

class ... {
Base *x;
};
 
class Base{};
template .... class X : public Base {...};

class ... {
Base *x;
};

class Base{};
template .... class X : public Base {...};

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[marcel]

I think you can avoid templates. Why not using only a factory class + an abstract(basically for preventing instantiating this meaningless class) node class + node implementations?
The factory class will return Node(abstract) objects which you could identify later by adding a getType pure virtual method which subclasses actually implement.

For example:

AbstractNode *node = NodeFactory.CreateNode...;
switch(node->type())
{
...
case AbstractNode::eTypeANode:
  {
    dynamic_cast<TypeANode*>(node)->SomeTypeANodeSpecializedMethod();
    break;
  }
...
}

AbstractNode *node = NodeFactory.CreateNode...;
switch(node->type())
{
...
case AbstractNode::eTypeANode:
  {
    dynamic_cast<TypeANode*>(node)->SomeTypeANodeSpecializedMethod();
    break;
  }
...
}

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[_borker_]

thanks Marcel, that looks like a good idea. From what you and wysota have said, steering clear of templates might well be the best idea here.

cheers
borker

[_borker_]

thanks for the reply

When the query is created the return type will be known so it's possible to know the desired return type at compile time that will be what is used as the template class.

I'm mainly searching for a way to implement a behavior pattern that is more or less generic without having to create subclasses that don't do much more than just handle different return types.

I'll have a play around this evening with what you mentioned in your reply and see if that solves my problems

cheers
borker

[jacek]

What "return types" are we talking about here? Maybe QVariant is what you need?

[_borker_]

hmm, never really played around with QVariants, might be an option there also... thanks jacek