Swift笔记（一）

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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

2、

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

3、Here is how to access the data inside the tuple:

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

You can reference each item in the tuple by its position in the tuple, starting with zero. Swift allows you to name the
individual parts of a tuple, so you to be explicit about what each part represents. For example:

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

If you want to access multiple parts of the tuple at the same time, you can also use a shorthand syntax to make it easier:

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

The code is equivalent to the following:

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

If you want to ignore a certain element of the tuple, you can replace the corresponding part of the declaration with an
underscore.

let (x, y, _) = coordinates3D

This line of code only declares 

x

 and 

y

.
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 the Option key
and clicking on the variable or constant's name.