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Typically, the base class template will take advantage of the fact that member function bodies (definitions) are not instantiated until long after their declarations, and will use members of the derived class within its own member functions, via the use of a cast; e.g.:
This was identified as a defect, and the wording was adjusted to allow such a member to appear anywhere a constant expression is required, without requiring an out-of-class definition. This includes array bounds, case expressions , static member initializers, and nontype template arguments .
A class template provides a specification for generating classes based on parameters. Class templates are generally used to implement containers. A class template is instantiated by passing a given set of types to it as template arguments. [5] The C++ Standard Library contains many class templates, in particular the containers adapted from the ...
Here the base class template will take advantage of the fact that member function bodies are not instantiated until after their declarations, and it will use members of the derived class within its own member functions, via the use of a static_cast, thus at compilation generating an object composition with polymorphic characteristics.
Another kind of template, a class template, extends the same concept to classes. A class template specialization is a class. Class templates are often used to make generic containers. For example, the STL has a linked list container. To make a linked list of integers, one writes list<int>. A list of strings is denoted list<string>.
The variadic template feature of C++ was designed by Douglas Gregor and Jaakko Järvi [1] [2] and was later standardized in C++11. Prior to C++11, templates (classes and functions) could only take a fixed number of arguments, which had to be specified when a template was first declared.
Private (or class-private) restricts access to the class itself. Only methods that are part of the same class can access private members. Protected (or class-protected) allows the class itself and all its subclasses to access the member. Public means that any code can access the member by its name.
Class templates are really meta-classes: they are partial abstract data types that provide instructions to the compiler on how to create classes with the proper data members. For example, the C++ standard containers are class templates. When a programmer uses a vector, one instantiates it with a specific data type, for example, int, string or ...