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Apparently, consteval is going to be a keyword in C++20. The cppreference page for it is currently blank. What is it going to be and how does it relate to constexpr?
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C++20 introduces the keyword consteval, which is used to indicate that a function must evaluate at compile-time, otherwise a compile error will result. Such functions are called immediate functions. In the above example, the first two calls to greater() will evaluate at compile-time.
A consteval function can only invoke a constexpr function but not the other way around. use fundamental data types as variables that have to be initialized with a constant expression. A consteval (constexpr) function cannot. have static or thread_local data.
A constexpr function is a function that can be invoked within a constant expression. A constexpr function must satisfy the following conditions: It is not virtual. Its return type is a literal type. Each of its parameters must be of a literal type.
constinit - asserts that a variable has static initialization, i.e. zero initialization and constant initialization, otherwise the program is ill-formed.
It declares immediate functions, that is, functions that must be evaluated at compile time to produce a constant. (It used to be spelled constexpr! in a previous revision of the paper.) In contrast, constexpr functions may be evaluated at compile time or run time, and need not produce a constant in all cases.
The adopted paper is P1073R3, which is not yet publicly available, but a previous revision is available and the introductory (motivation and high-level description) portion is about the same (except that the "Source Locations" section is deleted in R3).
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