RecommendAFriendTypeAliases.scala

object RecommendAFriend{
  type Validate = NewAccountDetails => Unit
  type FindCustomer = String => Option[User]
  type CreateCustomer = NewAccountDetails => User
  type ReferralPolicy = NewAccountDetails => User
  
  def apply(validate: Validate, findCustomer: FindCustomer, createCustomer: CreateCustomer, 
            referralPolicy: ReferralPolicy)
            (referrerId: Int, friendsAccountDetails: NewAcccountDetails) = {
    ...          
  }
}