Re: Howto: Is not derived by any...
On Mar 3, 4:06 am, Thomas Lehmann <t.lehm...@rtsgroup.net> wrote:
Hi!
When possible I would like to known whether I can implement to
check whether a given instance is not derived.... (let's see)
Assume we have deriving in following order A <- B <- C <- D.
A* instanceA = new A;
A* instanceB = new B;
A* instanceC = new C;
A* instanceD = new D;
assert(instanceA->isBase());
Of course I could provide a member to do so but - techniqual - I'm not
very happy because the truth is we have s.th. like "C" as "working"
class and we want to be able to say:
assert(instanceC->isNotDerived()); // I'm not forced to this
signature!
I'm not happy with the idea to call dynamic_cast for each derived
class!
Another idea might be to provide an id or class name so I could say:
assert(instanceC->className() == "C");
assert(instanceC->classId() == ClassC);
Those logic heavily depends on virtual methods and the rely that
everybody
who takes part in development returns the correct value...
In addition someone could fail in writing "c" instead of "C" (ok he
can use constants)
but not all classes are in the same library (using different headers,
different enums?).
I would prefer to find a mechanism as done in "code guru of the week
#71"!
Is there any way to this? Any other idea? A common approach?
{ edits: sig & banner removed. do not quote extraneous material. -mod }
typeid may be your solution.
But...
Is it too late to change the current approach, though? (Type
inspection in random places doesn't ring well).
If you have conditional logic of type (that, IMO, happens often):
if (object type is C)
do C-related stuff;
Instead of that, you could use mix-in inheritance, e.g.
struct CRelatedStuff
{
virtual void Run() = 0;
};
class C: public B, public CRelatedStuff
{
virtyal void CRelatedStuff::Run() { ... }
}
Then, on client side:
CRelatedStuff* pC = dynamic_cast<CRelatedStuff*>(instanceX);
if (pC)
pC->Run();
You may decide to split Run into more methods, too. Only thing you
need is an idea of the interface your thing has to the part of the
code that needs to do C-related stuff.
HTH.
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