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