Question

StackOverflow. My first post here.
I’ve come to D from C++ and MFC, which i’m using in my job – not only GUI stuff, but many MFC’s macro(DECLARE_DYNCREATE, etc.) and CObject class.
How i saw, in D we have std.Object class with factory method.

So, how to correctly rewrite this C++ code in D? if it is possible, of course.

class CPerson : public CObject 
{
    DECLARE_DYNAMIC( CPerson )
    // other declarations
};
IMPLEMENT_DYNAMIC( CPerson, CObject )
void DoSmthWithObject(const CObject* pObj)
{
    CPerson* pPerson = dynamic_cast<CPerson*>(pObj);
    ASSERT_VALID(pPerson);
    // Work with out CPerson object.
}

// Somethere in code create our CObject...
CObject* pMyObject = new CPerson;

// .. and do some strange things with it.
DoSmthWithObject(pMyObject);

Answer 1

Downcasts are already runtime-checked in D. Attempting to perform an invalid downcast will result in a null reference.

class A { }
class B : A { }
class C { }

unittest
{
    A a = new A();
    Object o = a;               // upcasts are implicit
    assert(o !is null);         // OK, all classes implicitly descend from Object
    assert(cast(A)o !is null);  // OK, same class
    assert(cast(B)o is null);   // Not allowed, B is subclass of A
    assert(cast(B)a is null);   // Ditto
    assert(cast(C)o is null);   // Not allowed, C is unrelated to A
    assert(cast(C)a is null);   // Ditto
    assert(cast(C)cast(void*)a !is null); // Use intermediate cast to
                                          // void* to bypass runtime checks
}