Since the specific class is just an implementation detail, we could change it out later if there was a need for different performance characteristics. For example, consider a class hierarchy based on simple scientific classification using Genus and Species: abstract class Animal safe_cast_generic_types.Yes, it can be pretty common and is one of the advantages of using a hierarchical class system. C++ Upcasting and Downcasting should not be understood as a simple casting of different data types. The next sample shows how you can use safe_cast to perform a downcast with a generic type. Downcasting is an opposite process, which consists of converting base class pointer (or reference) to derived class pointer. The following sample shows unboxing with value types and primitive types. In the below example, the method objectToString takes an Object parameter which is assumed to be of type String. Unboxing is a user-defined conversion, but unlike boxing, unboxing must be explicit-that is, it must be performed by a static_cast, C-style cast, or safe_cast unboxing cannot be performed implicitly. Downcasting is useful when the type of the value referenced by the Parent variable is known and often is used when passing a value as a parameter. Finally, we downcast the Animal reference back to a Dog reference and call the fetch method, which prints Dog is fetching to the console. We then call the makeSound method on this object, which prints Dog is barking to the console. Therefore, you can use safe_cast to unbox a value on the CLR heap. In the main method, we first upcast an object of type Dog to type Animal. Unboxing is defined as a compiler-injected, user-defined conversion. I^ pv = safe_cast(v) // boxing will occur, not UDC "operator I^" The next sample shows that boxing has priority over a user-defined conversion in a safe_cast operation. With the simple example above of polymorphism, you should be able to quickly understand what up-casting is, in fact we have already used up-casting in our example. A safe_cast boxes a value type variable that's on the native stack so that it can be assigned to a variable on the garbage-collected heap. The downcasting does not follow the is- a relation in most of the cases. It manually cast the base classs object to the derived classs object, so we must specify the explicit typecast. The following sample shows boxing with simple and user-defined value types. The Downcasting is an opposite process to the upcasting, which converts the base classs pointer or reference to the derived classs pointer or reference. We should be careful on the fundamental in every phase. It ends up that things get revisited or refactored. Hopefully, this would help and we should pay more attention for the basic since the basic was more likely to be forgotten. Therefore, you can use safe_cast to box a value on the CLR heap. Luckily, the basic idea of downcasting and upcasting had been corrected in our earlier discussion. V^ v2 = safe_cast(r) // should invoke UDCīoxing is defined as a compiler-injected, user-defined conversion. Upcast Definition: (a.) Cast up thrown upward as, with upcast eyes. safe_cast_udc.cppĬonsole::WriteLine("in operator R^(V& v)") Ĭonsole::WriteLine("in operator V^(R^ r)") The next sample shows how you can use safe_cast to invoke user-defined conversions. Unlike static_cast, safe_cast performs a dynamic check and throws InvalidCastException if the conversion fails. A downcast is safe only if the object that's addressed at runtime is actually addressing a derived class object. safe_upcast.cppĪ downcast is a cast from a base class to a class that's derived from the base class. The following sample shows how to perform an upcast, with safe_cast and without it. This cast is safe and does not require an explicit cast notation. UpcastingĪn upcast is a cast from a derived type to one of its base classes. For information about safe_cast in C++/CX, see safe_cast. This article shows how to use safe_cast in C++/CLI applications.
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