Ah sorry about that, thanks for the feedback! I can try to answer these here (and hopefully update the documentation as well when I get the chance):
- The problem is basically twofold. Part (a) is that there are no facilities for dealing with enums in C++. "Dealing with" could be anything, such as: bitwise-combining enums as flags, converting enums to/from strings, verifying that a given value is valid for an enum, decomposing flags into their constituent values, and anything else people might typically want to do with enums. Part (b) is that people end up manually writing enum-specific functions for these over and over again, and that often results in brittle and non-reusable code that quickly gets out of sync with the actual enum as it evolves over time (e.g., handwritten parsing code might stop working when a new member is added). This library aims to address most if not all of these problems.
- There are 3 main "tricks" I've used (and a ton of boilerplate on top of that): (a) I use the auto-return-type-with-hidden-friends trick to "tag" the enum with metadata for later retrieval, (b) I overload the comma operator to be able to utilize the same text for both the enum definition as well as for storing relevant metadata, and (c) I use constexpr string parsing to extract the enum names from the definition passed to the macro. Part (a) is confusing and better explained in the link I put in the credits. Part (b) is somewhat tricky but hopefully not too bad. Part (c) seems obvious in hindsight now that I mention it, but I haven't seen it used elsewhere in this manner. (Edit: While digging further just now, I found someone has indeed tried a similar approach with constexpr string parsing in [1], though it appears less comprehensive.)
- No other libraries that I'm aware of support all the features of this one. Typical restrictions include: limiting the ranges of the underlying values, limiting the number of enumerators to some amount, not supporting enum members with duplicate values, not supporting 'enum class', etc.
Hope this helps! If I can clarify anything else please let me know.
To my knowledge magic_enum has some severe limitations; for example, it limits the range of enum values, it cannot handle duplicate enum values, it uses compiler-specific hackes, etc. There is a list of them outlined at [1]. Before writing this library I did take a look around for existing ones (there's also wise_enum [2] for example), but I couldn't find any that supports all of the functionality implemented here.
Update: And I'm glad to see interest! I just updated the repo to add a parse_enum function for converting strings to enums as well.
It is amazing how much effort is going to simplify adding "enum_to_string(e)" support in C++ or C. What is the reason this not being part of C++ standard?
All proposals for this sort of functionality are rejected as they would be subsumed by generalized compile time reflection. Which has been brewing for around 10 years and it nowhere close to be standardized.
For me the worst case of such behavior was when the C++/WinRT team managed to deprecate C++/CX, with the excuse that similar tooling in Visual Studio would be possible without language extensions as soon as C++ would get reflection.
Nowadays I just keep myself to writing .NET, touching C++/WinRT as little as possible.
It needs to be a special kind of developer to love to write by hand, without any tooling support, what C++/CX reflection offered out of the box.
I think WG21's process is not well suited to this type of problem. To some extent the process can't be fixed, because WG21 is a JTC1 sub-committee and so it must have - for example - the trappings of democracy (which is a bit like having a requirement that your tractor wheels must somehow be made out of blancmange).
But I believe for this type of problem it can be clarifying to begin by identifying a handful of things you should be able to do, and then baking those in. This helps because now competing proposals for how to do compile time reflection have an example application. How does your proposal make the agreed enum-to-string syntax work ? It must do that or it's not a proposal to solve the problem we agreed we have. And meanwhile the ordinary programmers get the things everybody agrees they should be able to do because we're just arguing about how those things work, not whether they should be possible.
Without this constraint, such proposals tend to wander off, each showing how they're ideally suited for solving a problem they came up with, in a context they chose, using methods they prefer, and so illuminating nothing.
A Try operator, perhaps written ?? has been proposed for C++ 26. Even if it's agreed that C++ wants this feature, you can expect years of arguing about exactly how it should work. Rust got its own Try operator ? many years ago. But the conceptual underpinning for this operator (now as the core::ops::Try trait), is still unstable and has actually been re-designed twice in that time. Ordinary Rust programmers don't need to care, they got a working operator, and they'll continue to have a working operator, only the people who care deeply about this need to spend time discussing the finer details of how that operator should be implemented.
It's indeed a lot of boilerplate that this library can hopefully reduce (which was one of my main goals). I don't know for sure, but I can guess some reasons why the standard doesn't support it:
- The problem is somewhat underspecified. There are lots of degrees of freedom—what delimiters you support, what character encodings you support, what inputs to accept (numeric vs. names), how exactly to deal with flags, etc. These make a generic solution more involved. It's in some sense a more complex version of the problem of number parsing, which has had quite a long journey and is still not entirely ergonomic in C++. (Even std::from_chars only came out in C++17, for example.)
- Lack of more general reflection capabilities, especially ones that provide string metadata, especially at compile-time. Given reflection isn't coming in C++23, it might be a while before we get support on this front.
Just about every non-c++ implementation depends on reflection or compile time introspection. Neither of which are in C++. So people endlessly reinvent the wheel.
reflection is one of the C++'s committee's highest priority as they recognize it will solve a lot of problems people have. However they also know that details matter and so they need more time to get it right. C++ has more than enough cruft that doesn't quite fit together, there is no interest in adding more.
Indeed. I first wrote an enum-to-string macro back in the late 80s in C, and again in the late 90s for C++. And here we are in 2022... still writing enum-to-string macros and the like.
I've needed linked list more often than enum to string over my 20+ years in industry. (both combined is less than a handful) This is mostly about what problems I've had to work on.
I think linked list taught me more useful skills than enum to string, even though I had to figure out the later on my own. Which is the important part of education, does learning things directly or indirectly help you more in the long run.
* what the problem is that needs solving,
* how the lib solves it and how that's preferable over dealing with the problem another way,
* how it compares to other libs that solve the same problem.
Therefore my interest in using this for my own projects right now is unfortunately close to zero.