Swift 정리 #2 연산자

용어

• 단항연산자(Unary operator): 선행연산자(prefix, !b), 후행연산자(postfix, c!)
• 이항연산자(Binary operator): 2 + 3
• 삼항연산자(Ternary operator): 삼항조건연산자(ternary conditional operator, a ? b : c)

Assignment Operator(지정연산자) =

let b = 10
var a = 5
a = b // a is now equal to 10

let (x, y) = (1, 2) // x is equal to 1, and y is equal to 2

if x = y {
    // This isn't valid, because x = y doesn't return a value.
}

Compound Assignment Operators

var a = 1
a += 2 // a = a + 2

Arithmetic Operators(산술연산자)

1 + 2       // equals 3
5 - 3       // equals 2
2 * 3       // equals 6
10.0 / 2.5  // equals 4.0

Remainder Operator %

9 % 4    // equals 1
// 9 = (4*2) + 1(remainder)

-9 % 4   // equals -1

Unary Minus Operator -

let three = 3
let minusThree = -three       // minusThree equals -3
let plusThree = -minusThree   // plusThree equals 3, or "minus minus three"

Unary Plus Operator +

let minusSix = -6
let alsoMinusSix = +minusSix  // alsoMinusSix equals -6

Comparison Operators

1 == 1   // true because 1 is equal to 1
2 != 1   // true because 2 isn't equal to 1
2 > 1    // true because 2 is greater than 1
1 < 2    // true because 1 is less than 2
1 >= 1   // true because 1 is greater than or equal to 1
2 <= 1   // false because 2 isn't less than or equal to 1

let name = "world"
if name == "world" {
    print("hello, world")
} else {
    print("I'm sorry \(name), but I don't recognize you")
}

(1, "zebra") < (2, "apple")   // true because 1 is less than 2; "zebra" and "apple" aren't compared
(3, "apple") < (3, "bird")    // true because 3 is equal to 3, and "apple" is less than "bird"
(4, "dog") == (4, "dog")      // true because 4 is equal to 4, and "dog" is equal to "dog"

("blue", -1) < ("purple", 1)        // OK, evaluates to true
("blue", false) < ("purple", true)  // Error because < can't compare Boolean values

Ternary Conditional Operator ?:_

question ? answer1 : answer2

if question {
    answer1 // true
} else {
    answer2 // false
}

let contentHeight = 40
let hasHeader = true
let rowHeight = contentHeight + (hasHeader ? 50 : 20) // rowHeight is equal to 90

let contentHeight = 40
let hasHeader = true
let rowHeight: Int
if hasHeader {
    rowHeight = contentHeight + 50
} else {
    rowHeight = contentHeight + 20
} // rowHeight is equal to 90

Nil-Coalescing Operator ??

a ?? b

a != nil ? a! : b // a!: unwrapping

let defaultColorName = "red"
var userDefinedColorName: String?   // defaults to nil

var colorNameToUse = userDefinedColorName ?? defaultColorName
// userDefinedColorName is nil, so colorNameToUse is set to the default of "red"

userDefinedColorName = "green"
colorNameToUse = userDefinedColorName ?? defaultColorName
// userDefinedColorName isn't nil, so colorNameToUse is set to "green"

Range Operators

Closed Range Operator ...

for index in 1...5 {
    print("\(index) times 5 is \(index * 5)")
}
// 1 times 5 is 5
// 2 times 5 is 10
// 3 times 5 is 15
// 4 times 5 is 20
// 5 times 5 is 25

Half-Open Range Operator

let names = ["Anna", "Alex", "Brian", "Jack"]
let count = names.count
for i in 0..<count {
    print("Person \(i + 1) is called \(names[i])")
}
// Person 1 is called Anna
// Person 2 is called Alex
// Person 3 is called Brian
// Person 4 is called Jack

One-Sided Ranges

for name in names[2...] {
    print(name)
}
// Brian
// Jack

for name in names[...2] {
    print(name)
}
// Anna
// Alex
// Brian

for name in names[..<2] {
    print(name)
}
// Anna
// Alex

let range = ...5
range.contains(7)   // false
range.contains(4)   // true
range.contains(-1)  // true

Logical Operators

Logical NOT Operator !

let allowedEntry = false
if !allowedEntry {
    print("ACCESS DENIED")
}
// Prints "ACCESS DENIED"

Logical AND Operator &&

let enteredDoorCode = true
let passedRetinaScan = false
if enteredDoorCode && passedRetinaScan {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "ACCESS DENIED"

Logical OR Operator ||

let hasDoorKey = false
let knowsOverridePassword = true
if hasDoorKey || knowsOverridePassword {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "Welcome!"

Combining Logical Operators

if enteredDoorCode && passedRetinaScan || hasDoorKey || knowsOverridePassword {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "Welcome!"

Explicit Parentheses

if (enteredDoorCode && passedRetinaScan) || hasDoorKey || knowsOverridePassword {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "Welcome!"