Function can_reuse_memory

r/src/r_to_arrow.cpp:1216–1232

in some situations we can just use the memory of the R object in an RBuffer instead of going through ArrayBuilder, etc ...

// in some situations we can just use the memory of the R object in an RBuffer
// instead of going through ArrayBuilder, etc ...
bool can_reuse_memory(SEXP x, const std::shared_ptr<arrow::DataType>& type) {
  // TODO: this probably should be disabled when x is an ALTREP object
  //       because MakeSimpleArray below will force materialization
  switch (type->id()) {
    case Type::INT32:
      return TYPEOF(x) == INTSXP && !Rf_isObject(x);
    case Type::DOUBLE:
      return TYPEOF(x) == REALSXP && !Rf_isObject(x);
    case Type::INT8:
      return TYPEOF(x) == RAWSXP && !Rf_isObject(x);
    case Type::INT64:
      return TYPEOF(x) == REALSXP && Rf_inherits(x, "integer64");
    default:
      break;
  }
  return false;
}

// this is only used on some special cases when the arrow Array can just use the memory of
// the R object, via an RBuffer, hence be zero copy