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The usage of a function template saves space in the source code file in addition to limiting changes to one function description and making the code easier to read. 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.
In the C and C++ languages, such non-portable constructs are generally grouped into three categories: Implementation-defined, unspecified, and undefined behavior. [3] The exact definition of unspecified behavior varies. In C++, it is defined as "behavior, for a well-formed program construct and correct data, that depends on the implementation."
A function template is a pattern for creating ordinary functions based upon the parameterizing types supplied when instantiated. For example, the C++ Standard Template Library contains the function template max(x, y) that creates functions that return either x or y, whichever is larger. max() could be defined like this:
It will merely serve as a function argument type to distinguish the expressions from other types (note the definition of a Vec constructor and operator+ below). template < typename E > class VecExpression { public : static constexpr bool is_leaf = false ; double operator []( size_t i ) const { // Delegation to the actual expression type.
In object-oriented programming, the template method is one of the behavioral design patterns identified by Gamma et al. [1] in the book Design Patterns.The template method is a method in a superclass, usually an abstract superclass, and defines the skeleton of an operation in terms of a number of high-level steps.
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.
For C and C++, the compiler is allowed to give a compile-time diagnostic in these cases, but is not required to: the implementation will be considered correct whatever it does in such cases, analogous to don't-care terms in digital logic. It is the responsibility of the programmer to write code that never invokes undefined behavior, although ...
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":