An example regarding how Swift 5.1 Property Wrapper can be useful for a light Input Validation enforcement.

EmailValidated.swift

@propertyWrapper
struct EmailValidated {
    private(set) var defaultValue: String = ""

    var wrappedValue: String {
        get { defaultValue }
        set { defaultValue = maxLength(newValue) && isValid(newValue)
            ?
                newValue
            :
            "" }
    }

    init(wrappedValue initialValue: String) {
        self.wrappedValue = initialValue
    }
    
    private func isValid(emailAddress: String) -> Bool {
        let emailRegEx = "(?:[a-zA-Z0-9!#$%\\&‘*+/=?\\^_`{|}~-]+(?:\\.[a-zA-Z0-9!#$%\\&'*+/=?\\^_`{|}"
            + "~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\"
            + "x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[a-z0-9](?:[a-"
            + "z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5"
            + "]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-"
            + "9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21"
            + "-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])"

        let emailValidation = NSPredicate(format:"SELF MATCHES[c] %@", emailRegEx)
        return emailValidation.evaluate(with: emailAddress)
    }
    
    private func maxLength(_ emailAddress: String) -> Bool {
        guard emailAddress.count <= 80 else {
            return false
        }

        guard let domainKey = emailAddress.firstIndex(of: "@") else { return false }

        return emailAddress[..<domainKey].count <= 64
    }
}

User.swift

struct User {
    @EmailValidated var email: String
    var name: String
}

let validUser = User(email: "[email protected]", name: "Darthpelo")
let invalidUser = User(email: "sdf[]@gmail.com", name: "Darthpelo")