So I have a base class Base and a few child classes. What I want to do is have a base class constructor that creates a child class based on a string argument, like:
Base:Base(string class_name) {
switch(class_name) {
case "something":
*this = SomeChildClass(...);
...
}
}
This compiles and runs but the object doesn't have the characteristics of the child class and I don't understand why. Shouldn't this work?
You can't do this in a constructor, because a constructor always constructs an object of a particular type. However, it's quite a common pattern to do this using a factory function, perhaps like this:
class Base
{
public:
static std::unique_ptr<Base> create(const std::string &class_name) {
if (class_name == "something") {
return std::make_unique<SomeChildClass>();
}
}
};
Note that in general, polymorphism requires dynamic object allocation (or some very specific scenarios), hence the unique pointer as the return type.
create to be part of Base.
Basein your code?*this = new SomeChildClass(...);should not compile, since the left hand side is a reference and the right hand side is a pointer.:,switchon string, etc.