Conditionally Declaring an Enum at Runtime (C++) - c++

Question

I've come across some interesting findings relating to runtime detection that has spurred an interesting question. If I want to declare a global variable based off a condition, I can easily do so during pre-compilation with #ifdefs. However, this produces different binaries, and I am looking for a solution that can be realized during runtime so as to constrain behavior to a single binary.
Example
A classic example that I can perform with arrays or other data types (note, the data types here are all const and must remain so - mirroring the immutable behavior of an enum):
Original (Compile Time):
#ifdef CONDITION
static const int faveNums[] = {......};
#else
static const int faveNums[] = {******};
#endif
Modified (Run Time):
static const int conditonalFaveNums[] = {......};
static const int defaultFaveNums[] = {******};
static const int * const faveNums = IsConditionTrue() ? conditonalFaveNums : defaultFaveNums;
Common Pitfall (Scoping):
This is a common pitfall that will not work, as if/switch conditionals are scoped and therefore unable to be referenced later - thank goodness for the ternary operator!
if(IsConditionTrue())
{
static const int faveNums[] = {......};
}
else
{
static const int faveNums[] = {******};
}
Problem
However, the situation appears to change with enums. Let's try the run time solution, but with an enum this time:
enum conditionalFaveNums = {......};
enum defaultFaveNums = {******};
enum faveNums = IsConditionTrue() ? conditonalFaveNums : defaultFaveNums;
This will not compile.
Compile time defines (as with the first example) can solve this, but is there a way to solve this at run time by conditionally declaring a global enum in C++?

Answer 1

While you can't do exactly what you're asking - the difference between your array and enum examples being that the array is simply data, whereas the enum is a type, and type definitions must be resolvable at compile time - perhaps a more helpful answer is that this is a good thing.
Dynamic data should be represented in a dynamic data structure. std::set is a pretty close conceptual match to an enum, and provides many useful (and efficient) methods that may come in handy later. Even better might be defining an enum listing all possible values at compile time, and then dynamically constructing a set of these values based on runtime information. (The set is thus a proper subset of the enum's range.)

Answer 2

You cannot do this. Key points to remember:
Values of variables can be initialized differently based on run time information.
Types MUST be defined/set at compile time.
You can use
static const int * const faveNums = IsConditionTrue() ? conditonalFaveNums : defaultFaveNums;
since that says what faveNums is to be initialized to at run time, using run time information.
You cannot use
enum faveNums = IsConditionTrue() ? conditonalFaveNums : defaultFaveNums;
since that tries to define the type faveNums using run time information.