#include<stdlib.h>
#include<stdio.h>
#include<string.h>

struct generic_array; 
struct item_handlers {
	void (*printer)(void*);
	void (*item_changer)(void*);
	void (*set_item)(struct generic_array*, void*, size_t);
};

struct generic_array {
	struct item_handlers* handlers;
	void* first_item;
	size_t item_size;
	size_t item_count;
};

void print_all(struct generic_array *ga){
	for(int i = 0; i < ga->item_count; i++){
		ga->handlers->printer(ga->first_item + ga->item_size * i);
	}
}

void double_printer(void* item){
	printf("%lf\n", *(double*)item);
}

void double_changer(void *item){
	*(double*)item /= 2;
}

void generic_set_item(struct generic_array* ga, void* new_item, size_t position){
	memcpy(ga->first_item + ga->item_size * position, new_item, ga->item_size);
}

struct item_handlers double_handlers = {double_printer, double_changer, generic_set_item};

int main(){
	struct generic_array array_of_doubles = {&double_handlers, malloc(sizeof(double) * 10), sizeof(double), 10};
	*(double*)(array_of_doubles.first_item) = 5.628;
	*(double*)(array_of_doubles.first_item + array_of_doubles.item_size) = 543.1;
	*(((double*)(array_of_doubles.first_item)) + 2) = -30.2;
	double new_item = 16.743;
	array_of_doubles.handlers->set_item(&array_of_doubles, &new_item, 3);
	

	print_all(&array_of_doubles);
	

}