[Swift] try, try!, try?

try.swift

import Foundation

enum ThrowableError: Error { case BadError }

func doSomething(_ occursError: Bool) throws -> String {
    if !occursError {
        return "Everything is ok"
    } else {
        throw ThrowableError.BadError
    }
}
func doSomeOtherThing() {
    let resultA = try! doSomething(false)
    // let resultB = try! doSomething(true)
    // => 実行時エラー

    if let resultC = try? doSomething(true) {
        print(resultC)
    } else {
        print("error occurs")
    }

    do {
        let resultD = try doSomething(true)
    } catch {
        print("error occurs")
    }

}

doSomeOtherThing()