Learn SwiftUI (Day 9/100)

import Cocoa

// ## Function Closure

// The parameters have moved inside the braces, and the in keyword is there to mark the end of the parameter list and the start of the closure’s body itself
// example 1, closure that takes no parameter, return boolean
let demo = { () -> Bool in
    print("Paying an anonymous person…")
    return true
}

// example 2, closure that takes 2 params, return string

let payment = { (user: String, amount: Int) -> String in
    if user == "john" && amount == 10 {
        return "yes"
    }
    return "no"
}
print(payment("john", 8))

// Notice: We don't use parameter names when calling a closure.
// payment(user: "john", amount: 8) --> incorrect

// :warning: Closures cannot use external parameter labels.
/*
 var cutGrass = { (length currentLength: Double) in
    // this is an invalid closure
}
 */

// example 3, pass closure as function type parameter
let team = ["Gloria", "Suzanne", "Piper", "Tiffany", "Tasha"]
let captainFirstTeam = team.sorted(by: { (name1: String, name2: String) -> Bool in
    if name1 == "Suzanne" {
        return true
    } else if name2 == "Suzanne" {
        return false
    }

    return name1 < name2
})
print(captainFirstTeam)

// ## Trailing closure
// 1, swift can infer parameter and return types in closure when pass as func parameter
// 2, remove `(by:`, start the closure directly
let captainFirstTeam2 = team.sorted { name1, name2 in
    if name1 == "Suzanne" {
        return true
    } else if name2 == "Suzanne" {
        return false
    }

    return name1 < name2
}

// ## shorthand syntax with $0, $1, etc.
let captainFirstTeam3 = team.sorted {
    if $0 == "Suzanne" {
        return true
    } else if $1 == "Suzanne" {
        return false
    }
    return $0 < $1
}

// ## Take function as parameter
func makeArray(size: Int, using generator: () -> Int) -> [Int] {
    var numbers = [Int]()
    for _ in 0..<size {
        let newNumber = generator()
        numbers.append(newNumber)
    }
    return numbers
}

// ## Check point

/*
 Your input is this:
 let luckyNumbers = [7, 4, 38, 21, 16, 15, 12, 33, 31, 49]

 Your job is to:
 Filter out any numbers that are even
 Sort the array in ascending order
 Map them to strings in the format “7 is a lucky number”
 Print the resulting array, one item per line
 */

let luckyNumbers = [7, 4, 38, 21, 16, 15, 12, 33, 31, 49]
let result = luckyNumbers.filter({!$0.isMultiple(of: 2)}).sorted() .map({"\($0) is a luck number"})
for ele in result {
    print(ele)
}