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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 .
Example implementation of expression templates : An example implementation of expression templates looks like the following. A base class VecExpression represents any vector-valued expression. It is templated on the actual expression type E to be implemented, per the curiously recurring template pattern.
Although static_cast conversions are checked at compile time to prevent obvious incompatibilities, no run-time type checking is performed that would prevent a cast between incompatible data types, such as pointers. A static_cast from a pointer to a class B to a pointer to a derived class D is ill-formed if B is an inaccessible or ambiguous base ...
In class-based programming, downcasting, or type refinement, is the act of casting a base or parent class reference, to a more restricted derived class reference. [1] This is only allowable if the object is already an instance of the derived class, and so this conversion is inherently fallible.
The g++ compiler implements the multiple inheritance of the classes B1 and B2 in class D using two virtual method tables, one for each base class. (There are other ways to implement multiple inheritance, but this is the most common.) This leads to the necessity for "pointer fixups", also called thunks, when casting. Consider the following C++ code:
Virtual inheritance is a C++ technique that ensures only one copy of a base class ' s member variables are inherited by grandchild derived classes. Without virtual inheritance, if two classes B and C inherit from a class A, and a class D inherits from both B and C, then D will contain two copies of A ' s member variables: one via B, and one via C.
Existing Eiffel software uses the string classes (such as STRING_8) from the Eiffel libraries, but Eiffel software written for .NET must use the .NET string class (System.String) in many cases, for example when calling .NET methods which expect items of the .NET type to be passed as arguments. So, the conversion of these types back and forth ...
As another, more significant, example of compile-time loop unrolling, template metaprogramming can be used to create length-n vector classes (where n is known at compile time). The benefit over a more traditional length-n vector is that the loops can be unrolled, resulting in very optimized code. As an example, consider the addition operator.