SwiftUI Form with `PreferenceKey` based validation

gistfile1.txt

// MARK: - Preference Key Declaration

struct FormValidationPreferenceKey: PreferenceKey {
    static var defaultValue: [Bool] = []

    static func reduce(value: inout [Bool], nextValue: () -> [Bool]) {
        value += nextValue()
    }
}

// MARK: - `validate` viewmodifier

struct ValidationModifier : ViewModifier  {
    let validation: () -> Bool

    func body(content: Content) -> some View {
        content
            .preference(
                key: FormValidationPreferenceKey.self,
                value: [validation()]
            )
    }
}

// MARK: - These two extensions are just shorthands for adding modifiers

extension TextField   {
    func validate(_ flag : @escaping () -> Bool) -> some View {
        self
            .modifier(ValidationModifier(validation: flag))
    }
}

extension SecureField   {
    func validate(_ flag : @escaping () -> Bool) -> some View {
        self
            .modifier(ValidationModifier(validation: flag))
    }
}

// MARK: - Form Container Implementation

struct ValidatedFormContainerView<Content : View> : View {
    @State private var validationResults : [Bool] = []
    @ViewBuilder var content : (( @escaping () -> Bool)) -> Content
    var body: some View {
        content(validate)
            .onPreferenceChange(FormValidationPreferenceKey.self) { value in
                validationResults = value
            }
    }
    
    private func validate() -> Bool {
        validationResults.allSatisfy{ $0 }
    }
}

// MARK: ViewModel Implementation

class FormViewModel: ObservableObject {
    @Published var email = ""
    @Published var password = ""
    @Published var name = ""
    @Published var surname = ""

    func isEmailValid() -> Bool {
        matchesRegex(
            regex: "[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,64}",
            on: email
        )
    }

    private func matchesRegex(regex: String, on string: String) -> Bool {
        let predicate = NSPredicate(format: "SELF MATCHES %@", regex)
        return predicate.evaluate(with: string)
    }
}

// MARK: Example Form View Implementation

struct FormView: View {
    @StateObject var formViewModel: FormViewModel

    var body: some View {
        ValidatedFormContainerView { isValid in
            VStack {
                Text("Form")
                    .font(.headline)
                TextField("Email", text: $formViewModel.email)
                    .validate {
                        formViewModel.isEmailValid()
                    }
                    .disableAutocorrection(true)
                    .autocapitalization(.none)
                TextField("Name", text: $formViewModel.name)
                    .validate {
                        !formViewModel.name.isEmpty
                    }
                TextField("Surname", text: $formViewModel.surname)
                    .validate {
                        !formViewModel.surname.isEmpty
                    }
                SecureField("Password", text: $formViewModel.password)
                    .validate {
                        formViewModel.password.count > 10
                    }
                Spacer()
                Button {
                    if !isValid() {
                        return
                    }
                    print("Form Valid")
                } label: {
                    Text("Ok")
                        .cornerRadius(16)
                }
                .disabled(!isValid())
            }
        }
        .padding()
    }
    
}