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Templates are a feature of the C++ programming language that allows functions and classes to operate with generic types.This allows a function or class declaration to reference via a generic variable another different class (built-in or newly declared data type) without creating full declaration for each of these different classes.
// A class template to express an equality comparison interface. template < typename T > class equal_comparable {friend bool operator == (T const & a, T const & b) {return a. equal_to (b);} friend bool operator!= (T const & a, T const & b) {return! a. equal_to (b);}}; // Class value_type wants to have == and !=, so it derives from // equal_comparable with itself as argument (which is the CRTP ...
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 .
The C++ template construct used above is widely cited [citation needed] as the genericity construct that popularized the notion among programmers and language designers and supports many generic programming idioms. The D language also offers fully generic-capable templates based on the C++ precedent but with a simplified syntax.
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. C++11 allows template definitions to take an arbitrary ...
Expression templates thus allow programmers to bypass the normal order of evaluation of the C++ language and achieve optimizations such as loop fusion. Expression templates were invented independently by Todd Veldhuizen and David Vandevoorde; [ 2 ] [ 3 ] it was Veldhuizen who gave them their name. [ 3 ]
The Metacode extension to C++ (Vandevoorde 2003) [1] was an early experimental system to allow compile-time function evaluation (CTFE) and code injection as an improved syntax for C++ template metaprogramming. In earlier versions of C++, template metaprogramming is often used to compute values at compile time, such as:
Here, attempting to use a non-class type in a qualified name (T::foo) results in a deduction failure for f<int> because int has no nested type named foo, but the program is well-formed because a valid function remains in the set of candidate functions.