Beautiful C++: 30 Core Guidelines for Writing Clean, Safe, and Fast Code

Chapter 4.4

Con.5: Use constexpr for values that can be computed at compile time

From const to constexpr

Prior to C++11, const machinery was restricted to two things: qualifying a type as const, and thus any instance of that type as immutable, and qualifying a nonstatic member function such that *this is const in its body, like this:

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class int_wrapper {
public:
  explicit int_wrapper(int i);
  void mutate(int i);
  int inspect() const;

private:
  int m_i;
};

auto const i = int_wrapper{7}; // i is of type int_wrapper const
// i.mutate(5); // Cannot invoke non-const qualified
                // member function on const object
auto j = i.inspect(); // Assign from inspect

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