downcast

I have two classes: /*Switch.h*/ class CSwitch : public CDeviceEntity {} /*EndSystem.h*/ class CEndSystem : public CDeviceEntity {} but when I use: CDeviceEntity* dev = NULL; dev = topo->headList[i]->node; if ( DYNAMIC_DOWNCAST( CEndSystem, dev ) != NULL ) {} " DYNAMIC_DOWNCAST " always returns not NULL while dev is kind of class CEndSystem or class CSwitch . If use: /*Switch.h*/ class CSwitch : public CDeviceEntity { DECLARE_DYNAMIC(CSwitch) } and /*Switch.cpp*/ IMPLEMENT_DYNAMIC(CSwitch, CDeviceEntity) /*EndSystem.h*/ class CEndSystem : public CDeviceEntity { DECLARE_DYNAMIC(CEndSystem) }

I've got a very large and mature C++ code base that I'm trying to use SWIG on to generate a C# interface for. I cannot change the actual C++ code itself but we can use whatever SWIG offers in the way of extending/updating it. I'm facing an issue where a C++ function that is written as below is causing issues in C#. A* SomeClass::next(A*) The caller might do something like: A* acurr = 0; while( (acurr = sc->next(acurr)) != 0 ){ if( acurr isoftype B ){ B* b = (B*)a; ...do some stuff with b.. } elseif( acurr isoftype C ) ... } Essentially, iterating through a container of elements that, depending

What's the difference between these two code snippets: let cell = tableView.dequeueReusableCellWithIdentifier("cellId") as UITableViewCell? // vs let cell = tableView.dequeueReusableCellWithIdentifier("cellId") as? UITableViewCell Isn't the result exactly the same? In that code there's no difference, in both cases it evaluates to UITableViewCell? The real difference is: in the first case a downcast to UITableViewCell? is expected to always succeed (even if it's nil), so if dequeueReusableCellWithIdentifier returns something that's not an instance of UITableViewCell (or an instance of a class

protocol P : class { var value:Int {get} } class X : P { var value = 0 init(_ value:Int) { self.value = value } } var ps:[P] = [X(1), X(2)] for p in ps { if let x = p as? X { // works for a single variable ... } } if let xs = ps as? [X] { // doesn't work for an array (EXC_BAD_ACCESS) ... } If P is a class instead of a protocol, than the code works correctly. What's the difference between class and protocol? They're both implemented as pointers in the heap, aren't they? The above code can be compiled successfully, but crash at runtime. What does this EXC_BAD_ACCESS error mean? Thanks to

I would like to check whether an object (e.g. someObject ) is assignable (cast-able) to a variable of another type (e.g. SpecifiedType ). In Java, I can write: someObject instanceof SpecifiedType A related question is finding whether the runtime type of an object is equal to a another type. In Java, I can write: someObject.getClass().equals(SpecifiedType.class) How can this be done in Objective-C? mouviciel Try [myObject class] for returning the class of an object. You can make exact comparisons with: if ([myObject class] == [MyClass class]) but not by using directly MyClass identifier.

I have my base class as follows: class point //concrete class { ... //implementation } class subpoint : public point //concrete class { ... //implementation } How do I cast from a point object to a subpoint object? I have tried all three of the following: point a; subpoint* b = dynamic_cast<subpoint*>(&a); subpoint* b = (subpoint*)a; subpoint b = (subpoint)a; What is wrong with these casts? How do I cast from a point object to a subpoint object? You can't; unless either point has a conversion operator, or subpoint has a conversion constructor, in which case the object types can be converted