クロージャの省略型

雛形

var sum: (Int, Int) -> Int  
sum = { (x: Int, y: Int) -> Int in  
  return x + y
}
let a = sum(1, 2)// 3

return省略

var sum: (Int, Int) -> Int  
sum = { (x: Int, y: Int) -> Int in  
  x + y
}
let a = sum(1, 2)// 3

型の省略

var sum: (Int, Int) -> Int  
sum = { (x, y) in  
  x + y
}
let a = sum(1, 2)// 3

括弧の省略

var sum: (Int, Int) -> Int  
sum = { x, y in  
  x + y
}
let a = sum(1, 2)// 3

簡略引数名の利用

var sum: (Int, Int) -> Int  
sum = { $0 + $1 }
let a = sum(1, 2)// 3