Better Enums

Reflective compile-time C++11 enum library with clean syntax. For example:

ENUM(Channel, int, Red = 1, Green, Blue);

defines a type Channel. You can then do natural things like:

Channel channel = Channel::Green;

channel.to_string();            // Results in the string "Green"
channel.to_integral();          // Results in the int 2

Channel::_from_string("Red");   // Results in Channel::Red
Channel::_from_integral(3);     // Results in Channel::Blue

constexpr auto channel = Channel::_from_integral(3);
                                // Do it at compile time
constexpr auto channel = Channel::_max;
                                // Channel::Blue

for (Channel channel : Channel::_values) {
    // Iterate over all channels
}

...and more. See the project page and examples for a tutorial.

Installation

Simply add enum.h and enum_preprocessor_map.h to your project. The current version can be found at https://github.com/aantron/better-enums/releases.

enum_preprocessor_map.h can handle enums with up to 256 constants. If you have more, re-generate it by running something like:

./pp_map_gen.py enum_preprocessor_map.h 512

This only needs to be done once when the constant limit is exceeded. You don't need to do this on every build. I hope to remove the need for this completely in a future version.

Features

• Generated at compile time by constexpr functions and the preprocessor. pp_map_gen.py is only needed if you have an enum with more than 256 constants.
• Safe conversions between enums and integers and strings. 1-basic.cc
• Iterable collections of constants and names. 2-iterate.cc
• Range information, such as the number of constants defined and the maximum constant. 2-iterate.cc
• Switch case checking. 3-switch.cc
• Almost all operations are constexpr and can be used at compile time in your own constexpr code. 4-constexpr.cc
• Constant values can be set (Red = 1) and aliased (Favorite = Green), just like with built-in enums.
• Generating a large number of enums is faster than including a typical standard header like iostream – performance test included.
• Explicit choice of underlying representation type.
• Header-only.
• No dependencies besides the standard library.
• Tested on gcc 4.9 and clang 3.6.

The library compiles only with gcc and clang due to use of weak symbols and due to lagging C++11 support in msvc. It should ultimately be portable to msvc, since msvc has its own version of weak symbols. Everything else in the library is standard C++.

Contact

Don't hesitate to contact me about features (or bugs!): antonbachin@yahoo.com

Explanation

The ENUM macro specializes a template based around a regular enum declaration, though it is more similar to enum class in the degree of type safety. The following are spiritually equivalent:

ENUM(Channel, int, Red = 1, Green, Blue);
enum class Channel : int {Red = 1, Green, Blue};

ENUM(Depth, char, Indexed8Bit, HighColor, TrueColor);
enum class Depth : char {Indexed8Bit, HighColor, TrueColor};

See the full documentation.

Development plan

There are several areas that still need improvement.

• I will try to eliminate the need for pp_map_gen.py. The library will then consist of one file, enum.h.
• to_string can be made constexpr, like most of the rest of the code.
• Iterators over defined constants should be made random-access. This would allow constexpr functions to use them by adding 1 – the only way to advance them now is by mutating increment.
• Some enum types might have a sensible choice for a default constructor. The library should allow it to be customized.
• All safety checks are currently done by linear scans. This may be a performance problem for enum types with many constants.
• Better diagnostics for empty enums or too many constants.
• Conversions from integers and strings that don't throw exceptions, but indicate failure by some other means.

License

Better Enums is released under the BSD 2-clause license. See LICENSE.

History

The library was originally developed by the author in the winter of 2012-2013 at Hudson River Trading, as a replacement for an older generator called BETTER_ENUM.