Question

I have the following test:

TestGet(): _interface(), _db(_interface)
{
    _interface.get = mockGet;
}

which is used when testing this class:

class DB: public IDB
{
public:
   explicit DB(Interface_T& interface):
     _interface(interface)
   {
   }

   ...

private:
   Interface_T _interface;
};

Interface_T is a C interface implemented in a struct and passed to me from a C api. I wish to use the DB class as a wrapper around the C interface.

Notice however that DB copies the interface object to its member _interface. Therefore the line:

_interface.get = mockGet;

has no effect from the DB objects point of view although this was the intention when I wrote the test class. How would you rewrite TestGet() to remedy this error? How would you present to the client of the DB class that it copies the value passed to it?

Answer 1

Presuming that your intention is for TestGet to set a member on the Interface_T object used by DB, you can:

A. Defer construction of DB:

TestGet(): _interface(), _db(NULL)
{
    _interface.get = mockGet;

    // Using a raw pointer here for minimalism, but in practice
    // you should prefer a smart pointer type.
    _db = new DB(_interface);
}

B. If you have control over the Interface_T class, you could add a constructor that initializes Interface_T::get directly. Then you could do:

TestGet(): _interface(mockGet), _db(_interface)
{
}

C. If you have control over the DB class, you could change it to share ownership of the supplied Interface_T (e.g. through boost::shared_ptr), add a constructor as in B, or add an accessor to its internal Interface_T member.