Custom types for hints / error messages

[Bendzae]

Context

Currently a hint or errorMessage has to be a string. It would be great to be able to supply a custom type for these to allow a more flexibility in the we different applications might model their errors.

Proposed solution

• Introduce a new type parameter to the Validation class: Validation<T,E> where E is the type of the error format.
• Allow passing this type as a hint/errorMessage. Example:

  enum class CustomError(description: String, severity: Severity) {
  SOME_ERROR("This is some error", Severity.HIGH),
  SOME_OTHER_ERROR("This is some other error", Severity.MEDIUM),
  }
  Validation<MyClass, CustomError> {
  MyClass::someValue {
      min(0) hint CustomError.SOME_ERROR
  }
  }

Of course library default messages like "is required" would need to be customisable then (which would be a great feature anyways).

I would be more then happy to create a PR to implement this if it is something that could be considered 🙂

[dhoepelman]

Thanks for the proposal. Currently not interested in doing this for mainly 2 reasons:

1. It's a large breaking change to the API, would require much existing code to be rewritten
   • The alternative would be to add a second type, but this would bloat the API a lot
2. The primary purpose of this library is to validate with human-readable, not to handle different validation scenarios separately.

You can take a look at Arrow's Either, which has the customizable error type.

For the specific example given I would personally probably make a Validation per severity level, and then collect them using the ValidationResult.errors list with a severity attached

[Bendzae]

Alright that makes a lot of sense. Thank you for the quick reply and great work on konform anyways!