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In C++, classes can be forward-declared if you only need to use the pointer-to-that-class type (since all object pointers are the same size, and this is what the compiler cares about). This is especially useful inside class definitions, e.g. if a class contains a member that is a pointer (or a reference) to another class.
UML class diagram that illustrates forwarding. In this Java example, the Printer class has a print method. This print method, rather than performing the print itself, forwards to an object of class RealPrinter. To the outside world it appears that the Printer object is doing the print, but the RealPrinter object is the one actually doing the work.
Nested classes are also a feature of the D programming language, Visual Basic .NET, Ruby, C++ and C#. In Python, it is possible to nest a class within another class, method or function. C++ has nested classes that are like Java's static member classes, except that they are not declared with "static". BETA language introduced this notion of ...
Python. The use of the triple-quotes to comment-out lines of source, does not actually form a comment. [19] The enclosed text becomes a string literal, which Python usually ignores (except when it is the first statement in the body of a module, class or function; see docstring). Elixir
The curiously recurring template pattern (CRTP) is an idiom, originally in C++, in which a class X derives from a class template instantiation using X itself as a template argument. [1] More generally it is known as F-bound polymorphism , and it is a form of F -bounded quantification .
In languages such as Pascal that require declaration before use, mutually recursive functions require forward declaration, as a forward reference cannot be avoided when defining them. As with directly recursive functions, a wrapper function may be useful, with the mutually recursive functions defined as nested functions within its scope if this ...
In C++ pointers to non-static members of a class can be defined. If a class C has a member T a then &C::a is a pointer to the member a of type T C::*. This member can be an object or a function. [16] They can be used on the right-hand side of operators .* and ->* to access the corresponding member.
A related concept is inner types, also known as inner data type or nested type, which is a generalization of the concept of inner classes. C++ is an example of a language that supports both inner classes and inner types (via typedef declarations). [30] [31] A local class is a class defined within a procedure or function. Such structure limits ...