C-foldl

C Typesafe Varargs, in a sorta roundabout way.

Reasoning

I saw a possibility to make a CONCAT(...) macro that just worked with any amount of arguments. Down that path I found it could do so much more, and now it's a general purpose system for creating vararg functions/macros in C/C++.

Compilers Compatibility

Developed and tested on these compilers.

Clang 3.8.0
MSVC 19.00.23026
GCC 5.3.1

Files

FOLD.h is the library.
Generate_FOLD.c will generate FOLD.h

Properties

Return value must be the same as the first argument of the next function in the expansion.
Handles 0 arguments by expanding into nothing.
Handles 1 argument by expanding to that argument.
Handles 2 arguments by expanding into to a ordinary call.
More than 2 arguments and it will expand recursively.
Preprocessor macro is expanded properly with the inner calls first. And will work just fine as long as there is no exposed commas. Commas inside brackets are fine.

Sample

//Macro                   Expansion
FOLD(Func, a)          // a
FOLD(Func, a, b)       // Func(a, b)
FOLD(Func, a, b, c)    // Func(Func(a, b), c)
FOLD(Func, a, b, c, d) // Func(Func(Func(a, b), c), d)

// Directly make Func a vararg function
int Func_(int a, float b);
#define Func(...) FOLD(Func_, __VA_ARGS__)
//Macro             Expansion
Func(a)          // a
Func(a, b)       // Func_(a, b)
Func(a, b, c)    // Func_(Func_(a, b), c)
Func(a, b, c, d) // Func_(Func_(Func_(a, b), c), d)

// With preprocessor macro
#define CONCAT(a, b) a##b
//Macro                     Expansion
FOLD(CONCAT, a)          // a
FOLD(CONCAT, a, b)       // ab
FOLD(CONCAT, a, b, c)    // abc
FOLD(CONCAT, a, b, c, d) // abcd

// Or more simply
#define CONCAT_(a, b) a##b
#define CONCAT(...) FOLD(CONCAT_, __VA_ARGS__)
//Macro               Expansion
CONCAT(a)          // a
CONCAT(a, b)       // ab
CONCAT(a, b, c)    // abc
CONCAT(a, b, c, d) // abcd

EvineDev / C-foldl