sum.h

sum.h is a header-only library for generating and using tagged unions in c

How to use

The following code:

SUM(Foo, ((int, i), (char, c)));

results in this code being generated:

typedef enum Foo_Kind {
  Foo_INVALID = 0,
  Foo_i,
  Foo_c
};

typedef union Foo_Data {
  int i;
  char c;
};

typedef struct Foo {
  enum Foo_Kind kind;
  union Foo_Data data;
};

Refer to main.c for an example (albeit contrived) use-case of this library.

Warning

This library is in its infancy. There may be breaking API changes as more features get added.

Stripping prefixes

This library is loosely stb-like, especially in how it treats prefixes to avoid name collisions. However, if you find SUM_H_SUM(...) to be too verbose, defining SUM_H_STRIP_PREFIX before including sum.h makes the declaration into just SUM(...).

Other customization points:

SUM_H_DONT_GENERATE_INVALID_KIND_ENTRY

By default, sum.h will generate <Type>_INVALID = 0 as the first entry in the enum. This is useful to detect data that hasn't been properly intialized. define SUM_H_DONT_GENERATE_INVALID_KIND_ENTRY to disable this functionality

"Why did you do this that way?"

"Why Sum?"

I like the interpretation of algebraic data types when it comes to type theory and I needed a good name. I could have gone with variant, as C++ did, or any of the many other synoyms, but sum type was cute.

"Why is the enum 'Kind' and not 'Type'?"

'Type' is an overloaded term. Especially when in C++ where you actually might be passing around types. I find that saying "what kind of X is this?" instead of "what type of X is this?" disambiguates things.

"This only supports N fields. What if I have M > N?"

Near the top of sum.h, there is a block which contains the implementation details for generating the code it does. It can be expanded to your needs

Missing Features

• Generating "match", "contains", "get", "set" functions
• Maybe support structs defined within a SUM invocation? Would be useful for ergonomics when making return types but very difficult and magic-y. Not sure yet.
• Add SUM_R (name pending) for defining sum types as returns of functions
• Generating COUNT entries for enums?

Licensing

This library is free for use under the MIT license