gistfile1.swift

struct Person {
  let name: String
  func isValid() -> Bool {
    return !name.characters.isEmpty
  }
}

let validPerson = Person(name: "Tom")
let invalidPerson = Person(name: "")

validPerson.isValid() // => true
Person.isValid(validPerson)() // => true

invalidPerson.isValid() // => false
Person.isValid(invalidPerson)() // => false