第九天：闭包

https://www.hackingwithswift.com/100/swiftui/9

let sayHello = { (name: String) -> String in
    "Hi \(name)!"
}

这个sayHello的类型是(String) -> String。

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)

// 因为sorted函数的参数是闭包，且函数定义的时候已知闭包的类型，所以可以省略
let captainFirstTeam = team.sorted { name1, name2 in
    if name1 == "Suzanne" {
        return true
    } else if name2 == "Suzanne" {
        return false
    }

    return name1 < name2
}

// 可以进一步省略
let captainFirstTeam = team.sorted {
    if $0 == "Suzanne" {
        return true
    } else if $1 == "Suzanne" {
        return false
    }

    return $0 < $1
}

一些集合函数，经常可以使用$0，$1，$2来代表闭包的参数。 ```swift let uppercaseTeam = team.map { $0.uppercased() } print(uppercaseTeam) ``