CODEWITHSUNDEEP
c++inheritancec++11enums
Grief
Grief

Reputation: 2040

Separate enum declaration and definition in C++11

There are several questions on these forums about the inheritance of C++ enums for extending (which is actually the thing without the logic). But what about inheritance just for setting specific values? Currently, there is something like the following in my code:

//lib_impl.h
enum class X {
    a = 13, // these values are
    b = 42  // implementation dependent
}

//lib.h
#include "lib_impl.h"

void some_func(X param) {
    X x = X::a;
}

I just want to avoid the dependecy of the 'lib' from its implementation. Probably, something other than enums must be used for that. As even in C++11 we have the ability only to declare forward enum name, but not its enumerators:

//lib.h
enum class X { a, b } // this is both declaration and definition, unfortunately

void some_func(X param) {
    X x = X::a;
}

//lib_impl.h
#include "lib.h"

enum class X { // redefenition, compilation error
    a = 13,
    b = 42 
}

What is the best compile-time solution for such problems?

--

As it seems to be unimplementable in c++, what is the most common way to resolve such issues? Leave the dependency of the 'lib' from the 'impl' as it is? Probably, 'impl' could be split into two parts, small which will be included before the 'lib.h' and other, bigger, to be included after it. Is it ok or I need to abandon the use of enums in favor of abstract classes?

Upvotes: 3

Views: 1528

Answers (1)

Yakk - Adam Nevraumont
Yakk - Adam Nevraumont

Reputation: 275310

Expose an enum with nominal values (start with 0, sequential say). Inside your library, remap these values to an internal enum with implementation dependent values (say an array for speed, using the external value as index). Reverse the mapping if you export said enum values to the outside (the reverse mapping will be slower).

Upvotes: 2

Related Questions