Type-erased ValidatorType

AnyValidator.swift

protocol ValidatorType {
    typealias ValidatedType
    func isValid(object: ValidatedType) -> Bool
}

// You might want to make it a reference type, depending on your case.
struct AnyValidator<T>: ValidatorType {
    private let validatorBlock: (T) -> Bool
    
    init<V: ValidatorType where V.ValidatedType == T>(validator: V) {
        self.init(validatorBlock: validator.isValid)
    }

    private init(validatorBlock: (T) -> Bool) {
        self.validatorBlock = validatorBlock
    }

    func isValid(object: T) -> Bool {
        return self.validatorBlock(object)
    }
}