Even though we assume that the reader of this book is not a Design Pattern Denier, it's still a very good idea to remind ourselves why design patterns exist and why a successful framework such as Qt makes extensive use of different design patterns. Well, first of all, a design pattern is just one of many solutions to a software development task and it is not the only solution; and in fact, most of the times it's not even the fastest solution. However, a design pattern is definitely the most structured way of solving a software development problem, and it helps make sure you use some predefined template-like structures for everything you add to your program.
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Design patterns have names applied to different kinds of problems such as creating objects, how they run, how they handle data, and so on. Eric Gamma, Richard Helm, Ralph E. Johnson, and John Vlissides (referred to as the Gang of Four) describe many of the most widely used design patterns in their book titled Design...