pipeline code example

main.c

#include <assert.h>
#include <stdio.h>

typedef enum Input_type_t {
  inputTypeInt,
  inputTypeChar,
  inputTypeMax  // last
} InputType;

typedef struct Input_t {
  union {
    int i;
    char c;
  } v;
} Input;

// add one typedef for each supported type
typedef int (*intFunction)(int);
typedef char (*charFunction)(char);

typedef struct Callable_t {
  void* function;  // actual type depends on pipeline's input type
  struct Callable_t* next;
} Callable;

typedef struct Pipeline_t {
  const InputType inputType;
  Input input;  // initialized and used as accumulator
  Callable* const callableHead;
} Pipeline;


void _processInt(Pipeline *p) {
  Callable* c = p->callableHead;
  while (c) {
    // cast callable into the type we think it should be (fingers crossed! :))
    intFunction funPtr = (intFunction) c->function;
    p->input.v.i = (*funPtr)(p->input.v.i);
    c = c->next;
  }
}

void process(Pipeline *p) {
  assert(p);
  switch (p->inputType) {
    case inputTypeInt:
      _processInt(p);
      break;
    case inputTypeChar:
      // fall thru...
    default:
      assert(NULL); // not implemented
      break;
  }
}

int multiplyByTwo(int i) {
  return i * 2;
}

int subtractFive(int i) {
  return i - 5;
}

int main(void) {
  Callable c2 = { &subtractFive, NULL };
  Callable c1 = { &multiplyByTwo, &c2 };
  Input initial = { {.i=10} };
  Pipeline p = {inputTypeInt, initial, &c1};

  process(&p);
  printf("The pipeline initial input is %d and its result is %d\n",
	 initial.v.i, p.input.v.i);

  return 0;
}