Answer by HolyBlackCat for To evaluate constant in run time via function c++17

Using a function doesn't require moving evaluation to runtime. Just add constexpr to the function and it will work at compile-time.

const float _MOVEMENT_ = deg_to_rad(90); will work even without a constexpr function, with the function you have right now.

But it is advisable to:

• Make it static to share it across all instances of the class.

• Make it constexpr (to make things easier)

• Rename so that it doesn't use a reserved identifier (any identifier starting with _[A-Z] or containing __ is reserved).

• Not name it in uppercase since it's not a macro (C/C++ uses uppercase for macros by convention, other languages tend to use it for constants since C macros often were used as constants, but it's weird IMO to make a full circle and use it for all constants in C/C++).

  Same for the class name.

Overall, you end up with static constexpr movement = deg_to_rad(90);.