ManagedValidator(ManagedAttributeDescription attribute, Validate definition)

Creates an instance of this type.

Instances of this type are created by adding Validate metadata to ManagedObject properties.

Source 

ManagedValidator(this.attribute, this.definition) {
  if (definition._builtinValidate != null) {
    _build();
  } else {
    _validationMethod = definition.validate;
  }
}