我的主力博客：半亩方塘

1、In Swift,you can optionally use underscores to make larger numbers more human-readable. The quantity and placement of the underscores is up to you.

var variableNumber: Int = 1_000_000

var integer: Int = 100
var decimal: Double = 12.5
integer = decimal  // wrong
integer = Int(decimal)   // right

let coordinates: (Int,Int) = (2,3)  
let x: Int = coordinates.0  
let y: Int = coordinates.1  

let coordinatesNamed: (x: Int,y: Int) = (2,3)  
let x: Int = coordinatesNamed.x
let y: Int = coordinatesNamed.y  

let coordinates3D: (x: Int,y: Int,z: Int) = (2,3,1)
let (x,y,z) = coordinates3D  

let coordinates3D: (x: Int,1)
let x = coordinates3D.x
let y = coordinates3D.y
let z = coordinates3D.z  

let (x,_) = coordinates3D  

This line of code only declaresxandy. The_is special and simply means you are ignoring this part for now. You'll find that you can use the underscore throughout Swift to ignore a value.

4、Sometimes it's useful to check the inferred type of a variable or constant. You can do this in a playground by holding down theOptionkey and clicking on the variable or constant's name.