Add support for type-specific Validation based on Interface

[mvrahden]

• I have looked at the documentation here first?
• I have looked at the examples provided that may showcase my question here?

Package version eg. v9, v10:

v10

Enhancement:

Topic: Add support for Type-specific Validation based on Interface.

I'd like to propose to extend the required validation logic (under a new name, e.g. must) from a simple "Not Zero" check to contain an alternative path which would call an interface – if present – on the type and validate based on the implemented logic.

The interface could look like

type Validator interface { Validate() error }

Benefit with this interface: It is compatible with other validation libs as well.

Adding this validation, will allow to define custom type-specific validations and ensure their invocation based on the given tag (e.g. must).
If the validator interface is not defined on a type, the validation logic will fallback to the required validation logic.
Alternatively: The validation could also first perform the required validation and subsequently perform the interface based validation logic.

Feedback highly appreciated.

Similar Request: Issue 854

Code sample, to showcase or reproduce:

type SomeStruct struct {
  ID RID `validate:"must"`
}

type RID string

func (r RID) Validate() error {
  // type specific validation, just an example
  if !strings.HasPrefix(r, "_") {
    return errors.New("missing prefix \"_\"")
  }
  return nil
}