afaik only memcpy has that magic property, so I think parent is almost correct.

  void *p = malloc(n);
  *(int *)p = 42; // ok, *p is now an int.
  //*(float *)p = 3.14f; // I think this is not allowed, p points to an int object, regular stores do not change effective type
  float x = 3.14f;
  memcpy(p, &x, sizeof(float)); // but this is fine, *p now has effective type float

  pool->chunk_arr[i].next = &pool->chunk_arr[i + 1];

Later in pool_alloc:

  Chunk* result    = pool->free_chunk;
  ...
  return result;

  int *x = pool_alloc();
  *x = 42; // aliasing violation, *x has effective type 'Chunk' but tried to access it as an int*

  int *x = pool_alloc();
  memcpy(x, &(int){0}, sizeof(int)); // establish new effective type as 'int'
  // now we can do
  *x = 42;**