// *** before: ***
struct AdderOld {
    let base: Int
    func call(_ value: Int) -> Int { base + value }
}

let addOld = AdderOld(base: 10)
print(addOld.call(5))      // the name of the method was in the way at every use

// *** in version 5.2: ***
struct Adder {
    let base: Int
    func callAsFunction(_ value: Int) -> Int { base + value }
}

let add = Adder(base: 10)
print(add(5))              // callAsFunction is chosen by the compiler

// it may be overloaded, throwing, mutating and generic
struct Logger {
    var level = 0
    mutating func callAsFunction(_ message: String) { level += 1; print(
                          message) }
    func callAsFunction(_ number: Int) { print("number \(number)") }
}

// a stored closure would give the same call, but it cannot be overloaded
// and it is not a member of the type