Question

I need to port the following Java concept into C++ :

Hash map holding object id key and class type value:

 Map<String, Class> _objectsBank = new HashMap<>();

Somewhere in the init method I fill the bank like this:

    _objectsBank .put("CLASS_ID_1", MyClass1.class);
    _objectsBank .put("CLASS_ID_2", MyClass2.class);
    ....

Then , later ,I construct an instance of one of the classes saved in that bank by demand.
Kind of “lazy” init :

 private MyClass initNewProg(String name) {

    MyClass instance;


    try {

        Class cl = _objectsBank.get(name);
        java.lang.reflect.Constructor co = cl.getConstructor(String.class);
        instance= (MyClass) co.newInstance(name);
        return instance;

    } catch (NoSuchMethodException | SecurityException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e)
    {
        e.printStackTrace();
        return null;
    }
 }

How would I do it in C++ ? How can I set a class type as std::map value so that I can query it later to construct an appropriate instance from it?
Is there something like this in Boost libraries?

Answer 1

Take a look at Is there a way to instantiate objects from a string holding their class name? and Instantiating classes by name with factory pattern, which describe the problem and multiple approaches with pros & cons of each ones. The examples cover registration of contructors for classes, which solves the issue with multiple if-statements you mentioned in @Karthik T’s solution.