ErrorHandling.swift

import Foundation

// Error is protocol
// NSError is class
// NSError(domain: <#T##String#>, code: <#T##Int#>, userInfo: <#T##[String : Any]?#>)

enum BoardError : Error {
    case failed
    case resultPending
    case unknown
}

class CBSE {
    // Throwing function
    func getScore(seatNumber: Int) throws -> Int  {
        let percentage = Int.random(in: 0...100)
                
        if percentage < 35 {
            throw BoardError.failed
        } else {
            return percentage
        }
    }
}

let exam = CBSE()

// Do-Try?-Catch or Do-Try!-Catch catch not allowed
// Error: block is unreachable because no errors are thrown in 'do' block

// Do-Try-Catch
do {
   try exam.getScore(seatNumber: 23)
} catch {
    print(error)
}

// Try?
let score = try? exam.getScore(seatNumber: 4)

// Try! - Avoid using it
let score1 = try? exam.getScore(seatNumber: 3)

// Multiple case catch statement
do {
   try exam.getScore(seatNumber: 23)
} catch BoardError.failed, BoardError.resultPending {
    print("your result is pending for evaluation!!!")
} catch {
    print("unknown!!!")
}

// defer
func testDeferStatement() {
    defer {
        print(1)
    }
    
    defer {
        print(2)
    }
    
    defer {
        print(3)
    }
    
    do {
        print(4)
    }
    
    do {
        print(5)
    }
}

testDeferStatement()