Swift - 문법 (Values, Control Flow, Functions and Closures)

목차

Values

• var → variable
• let → constant
• type 명시 → `let explicitDouble: Double = 70`
• type conversion → wrap with `Int()`, `Double()`, `String()`
• String 표기 (string interpolation)
  • 기존 Flutter의 `'${value}'` -> Swift에서는 `"\(value)"`
• three double quotation marks(`"""`) → multiple line strings
• arrays and dictionaries → use `[]`
• array → var fruits = `["limes", "pears", "apples"]`
• dictionary → var jobs = `["Jae": "Student", "Kai": "Actor"]`

Control Flow

• conditionals → `if` and `switch`
• loops → `for-in`, `while`, `repeat-while`

for score in individualScores {
	if score > 50 {
    	teamScore += 3
    } else {
    	teamScore += 1
    }
}

Functions and Closures

• function → `func`
• use `->` to separate the parameter names and types from the function's return type

func greet(person: String, day: String) -> String {
    return "Hello \(person), today is \(day)."
}

• use underscore instead of an explicit argument label to omit the parameter

func someFunction(_ firstParameterName: Int, secondParameterName: Int) {}
someFunction(1, secondParameterName: 2)

• default parameter values

func someFunction(parameterWithoutDefault: Int, parameterWithDefault: Int = 12) {}
someFunction(parameterWithoutDefault: 3, parameterWithDefault: 6) // parameterWithDefault is 6
someFunction(parameterWithoutDefault: 4) // parameterWithDefault is 12

• function types

var mathFunction: (Int, Int) -> Int = addTwoInts

Define a variable called mathFunction, which has a type of ‘a function that takes two Int values, and returns an Int value.’ Set this new variable to refer to the function called addTwoInts.

• nested functions

func returnFifteen() -> Int {
    var y = 10
    func add() {
        y += 5
    }
    add()
    return y
}

• function can return another function as its value

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)

• closure → `({})`
• use in to separate the arguments and return type from the body in closure

numbers.map({ (number: Int) -> Int in
    let result = 3 * number
    return result
})

• if closure’s type is already known, can omit the type of its parameters, its return type, or both

let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)
// Prints "[60, 57, 21, 36]"

• when a closure is the only argument to a function, can omit the parentheses

let sortedNumbers = numbers.sorted { $0 > $1 }
print(sortedNumbers)
// Prints "[20, 19, 12, 7]"

 

Reference

Documentation