swift.md

Swift 5.3

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2020 12 8

// constant
let score = 66
score = 1 // error

// variable
var age = 11
age = 20

// specify type
var age:Int = 11

// concat string
let no = 22
let name = "Tom"
let nameAndNo = name + no // error
// 1
let nameAndNo = "name:" + name + ", no:" + String(no)
// 2
let nameAndNo = "name:\(name), no:\(no)"

// multiple lines
let lines = """
Use three double quotation marks (\"\"\") for strings that take up multiple lines.

Indentation at the start of each quoted line is removed, as long as it matches the indentation of the closing quotation marks.
"""

// To create an empty array or dictionary, use the initializer syntax.
let emptyArray = [String]()
let emptyDictionary = [String: Float]()


// not include upper value 3
for i in 0..<3 {
    print(i)
}
// 0,1,2

// include upper value 3
for i in 0...3 {
    print(i)
}
// 0,1,2,3


// 1. function definatin
func add(a:Double, b: Double)->Double {
    return a + b
}

print(add(a: 2, b: 1)) // 3.0

// 2. no label
func add(_ a:Double, _ b: Double)->Double {
    return a + b
}
print(add(2, 3)) // 5.0

// 3. custom label
func add(add a:Double, with b: Double)->Double {
    return a + b
}

print(add(add: 3, with: 4)) // 7.0

// A function can take another function as one of its arguments.

func hasAnyMatches(list: [Int], condition: (Int) -> Bool) -> Bool {
    for item in list {
        if condition(item) {
            return true
        }
    }
    return false
}
func lessThanTen(number: Int) -> Bool {
    return number < 10
}
var numbers = [20, 19, 7, 12]
hasAnyMatches(list: numbers, condition: lessThanTen)

// different between struct and class
// copy when passed
struct Data {
    var width = 200
}

let d0 = Data()
d0.width    // 200

var d1 = d0 // -copy-, create a copy
d1.width = 500  // if let d1, d1.width = 500 error
d1.width    // 500
d0.width    // 200

// passed by reference
class Model {
    var no:Int = 111
}

let m0 = Model()
m0.no   // 111
let m1 = m0 // -reference-, only one
m1.no = 222
m0.no   // 222
m1.no   // 222

Where usage in Swift