Have you ever wondered about a derived class whose base has access to the derived class members. We often find definitions of what crtp is, and it is indeed an intriguing construct. The curiously recurring template pattern crtp recently caught my attention as a nice trick which allows static polymorphism. In other words, it lets you build extensible classes without the overhead of virtual function calls. The curiously recurring template pattern crtp the crtp is a pattern which has many applications, but its main feature is that you can define a class which derives from a template class where the class being defined is itself a template type parameter. In short, crtp is when a class a has a base class which is a template specialization for the class a itself. The curiously recurring part refers to the fact that your class appears, rather curiously, in its own base class. What the curiously recurring template pattern reddit. A pattern is a familiar and instantly recognizable solution to specific problem. Since then, crtp has been popularized and is used in many libraries, particularly in boost. It works by having a base class template which takes, as one of its template parameters, the derived class. The curiouslyrecurring part refers to the fact that your class appears, rather curiously, in its own base class.
Better encapsulation for the curiously recurring template pattern. Templates curiously recurring template pattern crtp. Such a concern can be abstracted out in a manageable reusable module. This is doubly ironic, because the article was an instance of copliens column, the column without a name, and the name he assigned has got to be the strangest one in the patternverse. In this pattern, the base class for instance, matrixbase is in fact a template class, and the derived class for instance, matrix inherits the base class with the derived class itself as a template argument in this case, matrix inherits from. Polymorphic cloning and the crtp curiously recurring template patternkaty coe. The friend factory and the curiously recurring template. The pattern is characterized by a class with the definition. In particular, through the curiously recurring template pattern, its possible to implement a form of static polymorphism that closely mimics the syntax for overriding virtual functions. An introduction to inheritance and polymorphism handson. Curiously recurring template pattern expertsexchange. This is the problem we are facing, these are additional considerations that are most important in our case. It is curiously recurring, isnt it now, what does this give you. This is valid only if the size of x can be determined independently of t.
Provides students with a clear understanding of why, when, and how to use templates to build and maintain cleaner, faster, and smarter software more efficiently. The curiously recurring template pattern crtp section 16. The complete guide provides software architects and engineers with a clear understanding of why, when, and how to use templates to build and maintain cleaner, faster, and smarter software. The motivation for the crgp is to express a form of the template method design pattern. The curiously recurring template pattern crtp sandor. Prefer curiously recurring template pattern crtp to. What the curiously recurring template pattern can bring to. Basically, you create a templated base class which. Recently i came across a interesting design pattern, the curiously repeating template pattern crtp. Reusable approaches for objectoriented software design. The key to the technique is the strange template trickery thats being used. The pattern is a template class having a template type parameter derives from that type. A polymorphic collection of curiously recurring template.
Recall that the main idea of the crtp is that a class inherits from an instantiation of a base class template that is parameterized by the derived class type. Crtp is a technique to implement compiletime polymorphism. Implementing the method that will call to the wanted method implemented in the child class. Note the fbound polymorphism pattern being used myruntimeclass uses itself as a template argument to its base, myruntimeclasst. The curiously recurring template pattern crtp templates.
Better encapsulation for the curiously recurring template. A derived class inherits from the base class and customizes the behavior of the base class by overriding its virtual functions. A priori, there might be no reason to think that templates and inheritance interact in interesting ways. The solution is to use the commonlyused polymorphic cloning pattern. More generally it is known as fbound polymorphism, and it is a form of f bounded quantification. This is also called the curiously recurring template pattern crtp. In this manner, the friend factory can be employed together with the curiously recurring template pattern crtp that we studied in an chapter 7, the curiously recurring template pattern. Curiously recurring template pattern crtp crtp is a powerful, static alternative to virtual functions and traditional inheritance that can be used to give types properties at compile time. Specialize a base class using the derived class as a template argument. Why not use template nonmember functions that could operate on any class. With the help of the pattern you access the derived class public interface from the base class which helps you mostly. Aug 16, 2019 the curiously recurring template pattern is an interesting technique at least to know and sometimes to use.
However, it turns out that some interesting techniques combine these two features, including the curiously recurring. The technique was formalized in 1989 as f bounded quantification. Polymorphic cloning and the crtp curiously recurring template pattern by katy coe. Join us as we look at how it works along with a a discussion of complete vs incomplete types. Class hierarchies are used to express relationships and interactions between different parts of a software system, define and implement the interfaces between components, and. By addition of an aspect, substitutability with the original type is not broken so another motivation is to have a isa public inheritance or wasa private inheritance relationship with the type parameter. Creating a template class base that will be used as a base class. Jan 30, 2019 a pattern is a familiar and instantly recognizable solution to specific problem. Polymorphic cloning and the crtp curiously recurring. Instead, eigen achieves polymorphism with the curiously recurring template pattern crtp.
Other readers will always be interested in your opinion of the books youve read. Curiously recurring template pattern and statics in the base class. What the curiously recurring template pattern can bring to your code. This technique has a name its called curiously recurring template pattern crtp from. In this chapter, we describe a few of these techniques. One of the oldest is the curiously recurring template pattern crtp identified by james coplien in 1995. Aug 22, 20 the curiously recurring template pattern crtp the crtp is a pattern which has many applications, but its main feature is that you can define a class which derives from a template class where the class being defined is itself a template type parameter. But of course, with the limitation of compiletime resolving. Mar, 2019 the curiously recurring template pattern crtp march, 2019 in this article, we are going to discover the pattern that is called the curiously recurring template pattern. Discover the interesting ways that templates and inheritance interact by taking a close look at named template arguments, the empty base class optimization ebco, the curiously recurring template pattern crtp, and parameterized virtuality. If anything, we know from chapter that deriving from dependent base classes forces us to deal carefully with unqualified names. If you want to be able to apply all of these to a class, and you have the right type of order, you only. The curiously recurring template pattern handson design. This actually gives the x template the ability to be a base class for its specializations for example, you could make a generic singleton class.