enums that are really just sets of constants

[Murray Cumming <murrayc murrayc com>]

In the ABI-breaking versions of glibmm and gtkmm, we have recently
changed the enums to be C++11 "enum class"s. This is generally a
welcome improvement.
- Their values are, for instance, Things::ONE, rather than THINGS_ONE.
- Their values do not convert implicitly to other types such as int or
bool, helping the compiler to find some programmer mistakes.

We are also gradually moving the enums inside classes when they are
typically only used with that class.

However, some of the C enums that we wrap are actually meant to be
integer constants, so it seems that we cannot and should not use "enum
class" for these. So I wonder what is the most "modern C++" way to do
this while keeping the new-style syntax. Here are two possibilities:

1. Use old-style enums inside a class:

class ResponseType {
public:
  enum Enum {
    NONE = -1,
    REJECT = -2,
    ACCEPT = -3,
    ...
  };
};

But shouldn't we just avoid old-style enums completely?


2. Use constexpr int constants inside a class:

class ResponseType {
public:
  constexpr int NONE = -1;
  constexpr int
REJECT = -2;
  constexpr int ACCEPT = -3;
  ...
};

But shouldn't we use some kind of enum to group the values together?

-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com