Proposed 'pointer buffer' implementation - pointer buffers are extremely common in moarvm

buffer.c

#include <stdlib.h>

struct MVMPointerBuffer {
  union {
    void ** v;
    MVMObject **objects;
    MVMCollectable **collectables;
    MVMSpeshBB **spesh_bbs;
    /* some other common pointer types */
  } p;
  MVMint32 num;
  MMVint32 alloc;
};
typedef struct MVMPointerBuffer MVMPointerBuffer;

void MVM_pb_init(MVMPointerBuffer * buffer, MVMint32 initial_size) {
  buffer->p.v = calloc(initial_size, sizeof(void*));
  buffer->num = 0;
  buffer->alloc = initial_size;
}

void MVM_pb_append(MVMPointerBuffer * buffer, void * item) {
  if (buffer->num >= buffer->alloc) {
    buffer->alloc *= 2;
    buffer->p.v = realloc(buffer->p.v, buffer->alloc * sizeof(void*));
  }
  buffer->p.v[buffer->num] = item;
  buffer->num++;
}

void MVM_pb_destroy(MVMPointerBuffer * buffer) {
  free(buffer->p.v);
  buffer->alloc = 0;
  buffer->num = 0;
}