example.c

typedef struct{
  int count;
} base;

typedef struct{
  base root;
  int multiplier;
} leaf;

root* leaf_new(int multiplier){
  leaf* l = malloc(sizeof(leaf));
  l->root.count = 0;
  l->multiplier = multiplier;
  return &l->root;
}

void leaf_set_multiplier(root* r, int multiplier){
  leaf* l = container_of(r, leaf, root);
  l->multiplier = multiplier;
}