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An instantiated function template usually produces the same object code, though, compared to writing separate functions for all the different data types used in a specific program. For example, if a program uses both an int and a double version of the max() function template above, the compiler will create an object code version of max() that ...
The use of templates as a metaprogramming technique requires two distinct operations: a template must be defined, and a defined template must be instantiated.The generic form of the generated source code is described in the template definition, and when the template is instantiated, the generic form in the template is used to generate a specific set of source code.
For example, basic_fstream<CharT,Traits> refers to the generic class template that implements input/output operations on file streams. It is usually used as fstream which is an alias for basic_fstream<char,char_traits<char>> , or, in other words, basic_fstream working on characters of type char with the default character operation set.
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 ...
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 Standard Template Library (STL) is a software library originally designed by Alexander Stepanov for the C++ programming language that influenced many parts of the C++ Standard Library. It provides four components called algorithms , containers , functions , and iterators .
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 following is a declaration of the concept "equality_comparable" from the <concepts> header of a C++20 standard library. This concept is satisfied by any type T such that for lvalues a and b of type T, the expressions a==b and a!=b as well as the reverse b==a and b!=a compile, and their results are convertible to a type that satisfies the concept "boolean-testable":