Where is the best place to locate enum types?

Question

I have found that there is generally a singe type or namespace that takes in any particular enum as a parameter and as a result I have always defined those enums there. Rece

Answer 1

I use nested namespaces for this. I like them better than putting the enum within a class because outside of the class you have to use the full MyClass::MyEnum usage even if MyEnum is not going to clash with anything else in scope.

By using a nested namespace you can use the "using" syntax. Also I will put enums that relate to a given subsystem in their own file so you don't get dependency problems of having to include the world to use them.

So in the enum header file you get:

// MyEnumHeader.h
// Consolidated enum header file for this dll,lib,subsystem whatever.
namespace MyApp
{
  namespace MyEnums
  {
    enum SomeEnum { EnumVal0, EnumVal1, EnumVal2 };
  };
};

And then in the class header file you get:

// MyInterfaceHeader.h
// Class interfaces for the subsystem with all the expected dependencies.

#include "MyEnumHeader.h"

namespace MyApp
{
  class MyInterface
  {
  public:
    virtual void DoSomethingWithEnumParam (MyEnums::SomeEnum enumParam) = 0;
  };
};

Or use as many enum header files as makes sense. I like to keep them separate from the class headers so the enums can be params elsewhere in the system without needing the class headers. Then if you want to use them elsewhere you don't have to have the encapsulating class defs as you would if the enums were declared within the classes.

And as mentioned before, in the outer code you can use the following:

using namespace MyApp::MyEnums;