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In C++11, this technique is known as generalized constant expressions (constexpr). [2] C++14 relaxes the constraints on constexpr – allowing local declarations and use of conditionals and loops (the general restriction that all data required for the execution be available at compile-time remains).
The technique was formalized in 1989 as "F-bounded quantification."[2] The name "CRTP" was independently coined by Jim Coplien in 1995, [3] who had observed it in some of the earliest C++ template code as well as in code examples that Timothy Budd created in his multiparadigm language Leda. [4]
However, the arrival in C++11 of standard library features such as std::conditional has provided another, more flexible way to handle conditional template instantiation. // Induction template < unsigned N > struct Factorial { static constexpr unsigned value = N * Factorial < N - 1 >:: value ; }; // Base case via template specialization ...
std::make_unique can be used like std::make_shared for std::unique_ptr objects. [7] std::integral_constant gained an operator() overload to return the constant value. [16] The class template std::integer_sequence and related alias templates were added for representing compile-time integer sequences, such as the indices of elements in a ...
C++26 is the informal name for the version of the International Organization for Standardization (ISO) and International Electrotechnical Commission (IEC) 14882 standard for the C++ programming language that follows C++23. The current working draft of this version is N4981.
In C++20, the std::bit_cast function allows type punning with no undefined behavior. It also allows the function be labeled constexpr . constexpr bool is_negative ( float x ) noexcept { static_assert ( std :: numeric_limits < float >:: is_iec559 ); // (enable only on IEEE 754) auto i = std :: bit_cast < std :: int32_t > ( x ); return i < 0 ; }
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An alternative in both C and C++, especially in situations in which a pointer to the number is required, is to apply the const qualifier to a global variable. This causes the value to be stored in memory, instead of being substituted by the preprocessor. However, in modern C++ code, the constexpr keyword, introduced in C++11, is used instead: