Dont know what type of class I have after doing a

Question

I have this structure:

class IIterator : public ICollectible{};
class A: public ICollectible{};
class b: public A{};
class c: public A{};
class d: public A{};

When I do something like this

IIterator* it = colection->getIterator();
whatType* db = dynamic_cast<whatType*>(it->hasCurrent());

colection is list with elements of type A (it could have objects of type b, c or d) hasCurrent() gives me something type ICollectible, so I have to do

dynamic cast so I can work with b, c or d, but how do I know which one it is?

What is the point to mix your type if you need to know what is their true type ? — Stargateur, Jun 15 '17 at 23:12
Welcome to Stack Overflow. Please take the time to read [The Tour](http://stackoverflow.com/tour) and refer to the material from the [Help Center](http://stackoverflow.com/help/asking) what and how you can ask here. — πάντα ῥεῖ, Jun 15 '17 at 23:13

score 2 · Answer 1 · answered Jun 15 '17 at 23:15

2

The point of dynamic_cast is that it tells you if you have the right type, or it returns nullptr. So you can do:

if (b *p = dynamic_cast<b *>(it->hasCurrent())) {
    // its b
} else if (c *p = dynamic_cast<c *>(it->hasCurrent())) {
    // its c
} else if (d *p = dynamic_cast<d *>(it->hasCurrent())) {
    // its d
} else {
    // none of the above

Of course, many OO purists will consider this a "bad code smell" -- you should define a virtual function in your interface class and call that, rather than testing for different derived types.

answered Jun 15 '17 at 23:15

Chris Dodd

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I was doing that but seemed so terrible that thought there was another way – Marcos Ayala Jun 15 '17 at 23:28
@MarcosAyala that another way is to use polymorphism. Either via `std::function`, virtual dispatch or even function pointers. – Guillaume Racicot Jun 16 '17 at 03:23

Dont know what type of class I have after doing a

1 Answers1