The function creates an instance of Base, DerivedA or DerivedBbased on the provided name. Design Patterns: Elements of Reusable Object-Oriented Software 5 Preface to CD As we were writing Design Patterns, we knew the patterns we weredescribing had value because they had proven themselves in manydifferent contexts. An alternative solution when the virtualmethods calls performance overhead is not acceptable, is to usegeneric programming or templates which doesn't have runtime cost sincethe methods to be called are resolved at compile-time.Once the classes are registered, objects can be instantiated with:Decorator class for drawing a shape at some position by saving,changing and restoring the transformation matrix.In its fullest expression, type erasure is the process of turning awide variety of types with a common interface into one type with thatsame interfaceImplementation of FileRepository (FileRepository.cpp)Solution 1: Use a custom RAAI wrapper object.The visitor design pattern is a behavioral design pattern which allowsto add new operations to a class hierarchy without modifying classesor adding new methods to derived classes. Thisapproach has many advantages over constructor instantiation. Another benefit is that this techniqueallows objects to be instantiated in many different ways from severaldifferent data representation.Alternatives to Visitor Design Pattern:Example: All private members of class CashFlow are conained in theopaque type Impl which is not defined in the header file.Note: It is not a design pattern, but a technique for encodingmultiple booleans or flags inside a single value, passing multiplebooleans as function parameters or returning multiple booleans as asingle value.GOF: "Attach additional resposibilities to an objectdynamically. Namedconstructors are more readable than ordinary constructors and unlikeconstructors, many named constructors static methods sharing the sametype signature can coexist. Infact, by using std::visit, no class modification is required toimplement this pattern.Invoke default constructor of class DerivedB through the objectDerivedB:The parent abstract class has four different types of methods:Note: this design pattern is similar to a callback and can besimplified with functional programming.Note: The factory design pattern in this document is the variationwhich creates an instance of a set of derived classes based on someinput.Note: It is better to use the C++ file API since it is more C++friendly and already has RAII. While the visitor makeseasier to add new operators, it makes harder to add new derivedclasses.The idiom needs the following functions:Intent: A behavioral design pattern from GOF which allows the clientcode to select and change an algorithm encapsulated as an object atruntime.In this demonstration, it is presented a 2D stateful graphical APIsimilar to OpenGL or Windows' GDI which draws shapes on thescreen.
Design Patterns Lecture 5 .