使用宏“高阶函数"在 C 中进行函数式编程发电机 [英] Functional programming in C with macro "Higher Order Function" generators

问题描述

请注意，因为这是一个地狱般的问题;-)

Pay attention carefully because this is a hell of a question ;-)

我想在 C 中将模板函数用于泛型集合操作(​​如搜索、foreach 等)，同时保持编译器静态类型检查.当您使用像本例中这样的简单回调时，这是相当简单的:

I want to use template functions for generic collection actions (like search, foreach, etc.) in C while maintaining compiler static type checking. It is fairly straightforward while you're using simple callbacks like in this example:

#define MAKE_FOREACH(TYPE)
void foreach_##TYPE (TYPE[n] array, int n, void(*f)(TYPE)) {
  for(int i = 0; i < n; i++) {
    f(array[i]);
  }
}

因此您可以执行以下操作:

so you can do things like:

MAKE_FOREACH(int)
MAKE_FOREACH(float)

void intcallback(int x){
  printf("got %d
", x);
}

void floatcallback(float x){
  printf("got %f
", x);
}

int main(){
  int[5] iarray = {1,2,3,4,5};
  float[5] farray = {1.0,2.0,3.0,4.0,5.0};
  foreach_int(iarray, 5, intcallback);
  foreach_float(farray, 5, floatcallback);
}

如果我想实现带有返回类型的回调，例如创建一个map"函数，我可以这样做:

If I'd like to implement callbacks with return types, for example to make a "map" function, I could do:

#define MAKE_MAP(TYPE, RTYPE)
RTYPE* map_##TYPE (TYPE[n] array, int n, RTYPE(*f)(TYPE)) {
  RTYPE* result = (RTYPE*)malloc(sizeof(RTYPE)*n);
  for(int i = 0; i < n; i++) {
    result[i]=f(array[i]);
  }
}

到目前为止，一切都很好.现在问题来了，当我希望我的回调函数接受任意数量的类型参数时.

So far, so good. The problem comes now, when I want my callback functions to accept any number of typed arguments.

这个想法是这样的:

#define MAKE_MAP(TYPE, RTYPE, ...)
RTYPE* map_##TYPE (TYPE[n] array, int n, RTYPE(*f)(TYPE, __VA_ARGS__), __VA_ARGS__)
/*this would work for the declaration (because just the types would be enough)
but the  parameter names are missing :-s*/ 
{
  RTYPE* result = (RTYPE*)malloc(sizeof(RTYPE)*n);
  for(int i = 0; i < n; i++) {
    result[i]=f(array[i], /*here the names of the parameters, in order*/);
  }
}

所以，如你所见，我可以声明一个地图函数:

so, as you can see, I could declare a map function as:

MAKE_MAP(int, float, char)

给予:

float* map_int(int[n] array, int n, float(*f)(int, char), char);

但我无法弄清楚如何实现通过预处理器传递的参数.我在这里寻求您的帮助、想法和建议.

but I cannot figure how to implement the parameter passing with the preprocessor. Here is where I ask for your help, ideas and suggestions.

(顺便说一句，不要告诉我使用可变参数函数作为模板并将 va_list 参数传递给回调，因为所有这些都是因为类型检查:-p)

(By the way, don't tell me to use a variadic function as template and passing a va_list argument to the callback, because all this stuff was because of the type checking :-p)

推荐答案

如果您使用的是 Linux/BSD Unix，请查看 queue(3) 并检查 /usr/include/sys/queue.h - 之前已经完成了 :)

If you are on Linux/BSD Unix, take a look at queue(3) and check into /usr/include/sys/queue.h - it's been done before :)

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