code: func NewAttributeSourceFrom(input *AttributeSource) *AttributeSource {
  	assert2(input != nil, "input AttributeSource must not be null")
  	return &AttributeSource{
  		attributes:     input.attributes,
  		attributeImpls: input.attributeImpls,
  		_currentState:  input._currentState,
  		factory:        input.factory,
  	}
  }
docs: /* An AttributeSource using the default attribute factory */
  // func NewAttributeSource() *AttributeSource {
  // 	return NewAttributeSourceWith(DEFAULT_ATTRIBUTE_FACTORY)
  // }
  /* An AttributeSource that uses the same attributes as the supplied one. */