Is it possible to pass derived classes by reference to a function taking base class as a parameter
C++InterfaceC++ Problem Overview
Say we have an abstract base class IBase
with pure virtual methods (an interface).
Then we derive CFoo
, CFoo2
from the base class.
And we have a function that knows how to work with IBase.
Foo(IBase *input);
The usual scenario in these cases is like this:
IBase *ptr = static_cast<IBase*>(new CFoo("abc"));
Foo(ptr);
delete ptr;
But pointer management is better to be avoided, so is there a way to use references in such scenario?
CFoo inst("abc");
Foo(inst);
where Foo
is:
Foo(IBase &input);
C++ Solutions
Solution 1 - C++
Yes. You don't have to upcast your objects. All references/pointers to derived types are converted implicitly to base objects references/pointers when necessary.
So:
IBase* ptr = new CFoo("abc"); // good
CFoo* ptr2 = static_cast<CFoo*>(ptr); // good
CFoo* ptr3 = ptr; // compile error
CFoo instance("abc");
IBase& ref = instance; // good
CFoo& ref2 = static_cast<CFoo&>(ref); // good
CFoo& ref3 = ref; // compile error
When you have to downcast you may want to consider using dynamic_cast
, if your types are polymorphic.
Solution 2 - C++
You can cast an object just as you can a pointer. I remember this was common when converting char
to unsigned char
and various other sign changing casts in days of yore.