BaseFieldDefinition::setDefaultValueCallback

public BaseFieldDefinition::setDefaultValueCallback($callback)

public function setDefaultValueCallback($callback) {
  if (isset($callback) && !is_string($callback)) {
    throw new \InvalidArgumentException('Default value callback must be a string, like "function_name" or "ClassName::methodName"');
  }
  $this->definition['default_value_callback'] = $callback;
  return $this;
}