Range of enums in C++

Question

I'm confused with range of enums. I have code like this:

namespace regs {
enum Control_0 {
    THING1,
    THING2,
    THING3
};
enum Control_1 {
    THING100,
    THING200,
    THING300
};
const auto regs_range = {Control_0, Control_1}; //error
} // regs namespace

and need to itterate over this enums like range-based for:

for (const auto& reg : regs::regs_range) {
    get_register_data(reg);
}

I also need to save feature of acces of enum values like getThingData(Control_0::THING1)

Is it possible to implement this somehow?

For itterating over values in enum I've always used this : const auto regs_values_range = {Control_0::THING1, Control_0::THING2, Control_0::THING3}; but in relation to range of enums it's error.

Answer 1

This line:

const auto regs_range = {Control_0, Control_1};

Attempts to create a collection of types (Control_0 and Control_1), not values.
This is invalid.
Also note that Control_0 and Control_1 are distinct and unrelated types and so you cannot put values from them in a trivial way in one collection.

The proper solution depends on what you actually need to achieve:

1. If you need to represent a value that can be either one of the entries from Control_0 or the entries from Control_1, you can use std::variant:

   std::variant<Control_0, Control_1>
   

2. If on the other hand you would like to represent a value which is a pair - one entry from Control_0 together with one entry from Control_1, you can use one of the following:
   (1) std::tuple:

   std::tuple<Control_0, Control_1>
   

   (2) std::pair

   std::pair<Control_0, Control_1>
   

   (3) Create your own type holding one of each:

   struct Control_0_1
   {
       Control_0 ctrl0;
       Control_1 ctrl1;
   };
   

   IMHO option (3) is the best in this case as it will make your code clearer.

Finally you can store any of the above in a container (e.g. std::vector or any other) and iterate over them.

Answer 2

but in relation to range of enums it's error.

The problem is that Control_0 and Control_1 are types not values so const auto regs_range = {Control_0, Control_1} is invalid.

std::tuple<Control_0, Control_1> might suit more for your problem.