Hello Sven.
Wonderful project, well done!

Motivation

I believe it would be a nice addition to implement support for reporting validation errors. It can be helpful, for example, when you want to display a related error message to the user.

Solution

I played around with the project in a fork. I would love to implement the changes myself and submit a PR, but wanted to first do a proposal and open a discussion.

There are a couple of ways to do it. What first comes to my mind would be this:

• Let's say that we have a special struct to report our errors:

public struct ValidationError: Error {
    let localizedMessage: String
    ...
}

• The validation closure could return a Result<Value, ValidationError>, instead of a Bool.

• The property wrapper could include a validationError optional property that receives values upon validation and gets set to nil when restore() is called.

• When using, we would be able to check for a validationError and if there isn't any, we can go ahead and use the value.

Here's a rough example:

public extension Validation where Value == String {

    static var isValidPassword: Validation {
        return .init { (value) -> Result<String, ValidationError> in
            if value.count < 6 {
                return .failure(ValidationError(localizedMessage: "Password is too short. Minimum character count is 6."))
            }

            /* Additional checks

                ...

            */

            return .success(value)
        }
    }

}

if let errorMessage = $passwordInput.validationError?.localizedMessage {
    UserNotification.displayError(message: errorMessage)
    return 
}

// Safe to continue and use the passwordInput string

Additional Remarks

This feature would require quite some changes, but all of them would be internal to the API, meaning that the users of it won't have to change anything when using the default provided validations. However, their custom ones will have to be rewritten to return Results, instead of Bools.

All of this is a result of a small pre-lunch brainstorm. I'm sure there is a way to improve it 😄 Let me know what you think :)

ValidatedPropertyKit Environment

• ValidatedPropertyKit version: 0.0.4
• macOS version: 11.0.1
• Xcode version: 12.2
• Dependency manager (Carthage, CocoaPods, SPM, Manually): SPM

What did you do?

I have
@Validated(.isEmail) var email: String? { didSet { emailError = _email.isValid } }
in an ObservableObject
In a view I have a TextField linked to email

What did you expect to happen?

I expected the emailError to contains a bool & email to contains the text that was typed.

What happened instead?

emailError do contains a bool but it's always false because when I type, the letter disappears.
The value is present when I call willSet but isn't anymore in the didSet.
If I remove the call to isValid it works.

It works as expected on devices running 14.1 or lower but not on devices running 14.2

Do you have any example of using Validated package with SwiftUI, specially in the case of TextField.

How can I provide a custom message for validation like:

Validated(.nonEmpty("Username cannot be empty"))
var username: String?

Where can I provide "Username cannot be empty" message?

Is your feature request related to a problem?

Yes, the problem is that I can't use two wrappers at once. @validated and for example @published

What solution would you like?

Maybe new wrapper that wraps both @validated and @published. @ValidatedPublisher or something like that

What alternatives have you considered?

None so far

Any additional context?

@published
@validated(.range(8...))
var exampleField = ""

or

@binding
@validated(.range(8...))
var exampleField = ""

Please update the docs to add a real world example. Even after reading the docs for 10 times it is hard to understand what and how to use this library.

Cool repo ;-)
I haven't seen the usage of AnyValidatable struct anywhere, though.

Motivation

It could be really cool if we could use @validated on UITextField and UITextView to simplify form validation.

Solution

I don't have any solution yet but the purpose is to have :
@Validated(.nonEmpty) var myTextField: UITextField
@Validated(.hasPrefix("prefix") var myTextView: UITextView

And to have a new class Validator which can validate a list of specific @validated.
let validator = Validator()
validator.add(myTextField)
validator.add(myTextView)
let isFormValid = validator.isValid()

Additional context

I use UITextField as example but it could be applied to any UIKit components, example:
@Validated(.isOn or .ifOff) var mySwitch: UISwitch
@Validated(.range(13...)) var myStepper: UIStepper

I'm not sur if it's possible to easily adapt your code to UIKit components.

Motivation

ℹ Please replace this with your motivation. For example if your feature request is related to a problem.

Solution

ℹ Please replace this with your proposed solution.

Additional context

ℹ Please replace this with any other context or screenshots about your feature request (optional).

Motivation

ℹ My app needs to support iOS 13 and this package requires 14

Solution

ℹ There only seems to be one incompatible thing, which is the use of @StateObject in Validated

Additional context

ℹ This doesn't look like it's too difficult of a change. Would it be a case of changing the @StateObject to maybe an @ObservedObject and calling it a day?

ValidatedPropertyKit Environment

• ValidatedPropertyKit version:
  0.0.5

• macOS version:
  11.6.2

• Xcode version:
  13.2.1

• Dependency manager (Carthage, CocoaPods, SPM, Manually):
  SPM

What did you do?

I'm using a view model.

import CoreData
import Foundation
import ValidatedPropertyKit

extension EditView {
    class ViewModel: NSObject, ObservableObject {
        let item: Item
        let add: Bool
        let hasRelationship: Bool

        private let dataController: DataController

        @Validated(!.isEmpty)
        @Published var title = "" <= error
        // @Published var title: String <= error 

What did you expect to happen?

To access the variable as shown in the readme examples.

What happened instead?

Error....

Referencing initializer 'init(wrappedValue:_:nilValidation:)' on 'Validated' requires 
that 'Published<String>' conform to 'Optionalable'

I'm not sure why this is occurring?

Thanks in advance.

Motivation

There are many occasions where you have non nil Published variables in SwiftUI's ViewModel, validation of this kind of fields would be a nice addition.