constexpr
functions will be evaluated at compile time when all its arguments are constant expressions and the result is used in a constant expression as well. A constant expression could be a literal (like 42
), a non-type template argument (like N
in template<class T, size_t N> class array;
), an enum
element declaration (like Blue
in enum Color { Red, Blue, Green };
, another variable declared constexpr, and so on.
They might be evaluated when all its arguments are constant expressions and the result is not used in a constant expression, but that is up to the implementation.