CODEWITHSUNDEEP
c++
Rollie
Rollie

Reputation: 4752

Can methods be added to an object?

So we have a class, Customer. I don't have any choice but to use Customer to represent any Customer I have, including in the signature of any methods, etc I write. But my data is slightly different; I still want much of the functionality inside Customer, but some fields I need to sorta bastardize for my special case. Example:

class Customer
{
public:
  string GetName();
  void SetName(string _name);

  string GetAge();
  void SetAge(string _age);

protected:
  string name;
  string age;
};

class SpecialCustomer : public Customer
{
public:
  string GetAddress();
  void SetAddress(string _address);
}

So this all seems rather simple, but the problem I have is I am forced to pass around Customers. But as luck would have it, in my special case, I don't need age at all! So what I need to do is re-use the age data member to hold my address. Yes, I know it's bad. No, I can't change the requirements - my special data has to fit into a Customer object.

So to do this, I could of course just construct a SpecialCustomer from a Customer, but I'd like to avoid the copy. (edit: Also, many data members are exposed directly publicly, so I can't use composition and support their use) Instead, I considered making SpecialCustomer a wrapper, exposing the pieces of functionality I want. The problem is the real implementation of Customer is not trivial - it's be a bit of work to re-implement the whole interface, minus the fields I don't want.

The only way that jumps to mind to achieve this is with something like this:

void foo (Customer & _c)
{
  SpecialCustomer & sc = reinterpret_cast<SpecialCustomer &>(_c);
}

Obviously if SpecialCustomer has any virtual methods or data members, this won't work. But what if it is just a set of methods I want available on the object? Is there a better alternative to achieve this functionality?

Upvotes: 1

Views: 94

Answers (2)

user1174627
user1174627

Reputation: 57

Seems like your hands are tied from using OO techniques. How about using plain old non-member functions of the form

string getSpecialCustomerAddress (Customer & _c)
{
  return _c.GetAge();
}

You still have the problem of determining whether or not a customer is special

Upvotes: 1

TinyTheBrontosaurus
TinyTheBrontosaurus

Reputation: 4810

This ought to do it, using composition instead of inheritance.

class SpecialCustomer {
public:
    SpecialCustomer(Customer&) : _customer(customer) {}

    string getAge() { return customer.GetAge(); }

private:
    Customer& _customer;

}

No casting is needed at this point. Rather instantiating the wrapper class will be adequate.

Usage:

void foo (Customer & _c)
{
    SpecialCustomer sc(_c);
}

Upvotes: 0

Related Questions