Converting Boolean value to Integer value in Swift

Question

I was converting from Swift 2 to Swift 3. I noticed that I cannot convert a boolean value to integer value in Swift 3.

let p1 = ("a" == "a") //true

print(true)           //"true\n"
print(p1)             //"true\n"

Int(true)             //1

Int(p1)               //error

For example these syntaxes worked fine in Swift 2. But in Swift 3, print(p1) yields an error.

The error is error: cannot invoke initializer for type 'Int' with an argument list of type '((Bool))'

I understand why the errors are happening. Can anyone explain what is the reason for this safety and how to convert from Bool to Int in Swift 3?

Yarkand

For Swift 4, see my accepted answer for a similar question. – Kosse

Answer 1

Swift 5

Bool -> Int

extension Bool {
    var intValue: Int {
        return self ? 1 : 0
    }
}

Int -> Bool

extension Int {
    var boolValue: Bool {
        return self != 0 
    }
}

Ballinger

Beat me to it! This is definitely my preferred solution. It adheres to Swift conventions more than other solutions here. – Chigetai

And to go in the opposite direction (Int -> Bool) https://mcmap.net/q/374822/-converting-int-to-bool – Indiscernible

Never thought to solve it this way. This is quite good. Works like NSNumber. – Rout

Amazing mate. You have just saved me some time and head-scratching :) – Turkoman

Answer 2

You could use the ternary operator to convert a Bool to Int:

let result = condition ? 1 : 0

result will be 1 if condition is true, 0 is condition is false.

Edo

Ok, so casting from Boolean to Integer value is a no go in swift 3? – Yarkand

I don't believe this conversion was really ever part of Swift. I believe it was a side-effect of implicit conversions through NSNumber. Implicit Bool/Int conversions are an old source of bugs in C (in particular, because non-zero numbers like "2" is "true-ish" but not equal to true). Swift has actively tried to avoid these historic sources of bugs. – Hawser

Answer 3

Try this,

let p1 = ("a" == "a") //true
print(true)           //"true\n"
print(p1)             //"true\n"

Int(true)             //1

Int(NSNumber(value:p1)) //1

Cryptomeria

Seems deprecated – Jasper

Answer 4

EDIT - From conversations in the comments, it is becoming clearer that the second way of doing this below (Int.init overload) is more in the style of where Swift is headed.

Alternatively, if this were something you were doing a lot of in your app, you could create a protocol and extend each type you need to convert to Int with it.

extension Bool: IntValue {
    func intValue() -> Int {
        if self {
            return 1
        }
        return 0
    }
}

protocol IntValue {
    func intValue() -> Int
}

print("\(true.intValue())") //prints "1"

EDIT- To cover an example of the case mentioned by Rob Napier in the comments below, one could do something like this:

extension Int {
    init(_ bool:Bool) {
        self = bool ? 1 : 0
    }
}

let myBool = true
print("Integer value of \(myBool) is \(Int(myBool)).")

Katmandu

Or combine @eric-aya 's ternary op recommendation with a protocol for maximum conciseness! – Katmandu

This approach has generally been discouraged by the core Swift team. They recommend Int.init overloads rather than methods to perform full-width conversions. – Hawser

Any documentation I could read to that effect @Rob-napier? I'd like to know more about why it's discouraged and the discussion leading to that decision. – Katmandu

I can't put my hands on a conversation right now; buried somewhere in swift-evo. But you can see the results of the opinion by watching how stdlib has evolved. For example, see github.com/apple/swift-evolution/blob/master/proposals/… and note where ...value methods have been converted to init (there were never many ...value methods in stdlib, but see ObjectIdentifier and StaticString). Note also in the Swift 3 style guidelines that type conversions are only discussed in terms of init's. Never methods. – Hawser

Cool, more curious than anything. Thanks! – Katmandu

I wish I could put my hands on a specific "here is the history," but it's much more "every time I bring up .array on LazySequence to replace Array.init, I'm reminded by one of the team that there is a preference for init. – Hawser

Answer 5

Swift 5.4

This is a more generic approach which is applicable for other types than just Int.

extension ExpressibleByIntegerLiteral {
    init(_ booleanLiteral: BooleanLiteralType) {
        self = booleanLiteral ? 1 : 0
    }
}

let bool1 = true
let bool2 = false

let myInt = Int(bool1) // 1
let myFloat = Float(bool1) // 1
let myDouble = Double(bool2) // 0
let myCGFloat = CGFloat(bool2) // 0

Postliminy

Answer 6

unsafeBitCast is always an option

let int: Int = Int(unsafeBitCast(someBool, to: UInt8.self))

Manhandle

Offering an explanation is always useful on Stack Overflow, but it's especially important where the question has been resolved to the satisfaction of the community. Help readers out by explaining what your answer does different and when it might be preferred. Can you edit your question to add more detail? – Concertina

That doesn't seem safe – Inwardness

Answer 7

You could use hashValue property:

let active = true
active.hashValue // returns 1
active = false
active.hashValue // returns 0

Gipon

If you do this in Swift 4.2, you are going to get values like 482808648934333090 and similar. – Everyplace

Yes, you can look at this Q&A https://mcmap.net/q/374823/-bool-hashvalue-valid-to-convert-to-int/4711785 – Bulk

Answer 8

Tested in swift 3.2 and swift 4

There is not need to convert it into Int

Try this -

let p1 = ("a" == "a") //true

print(true)           //"true\n"
print(p1)             //"true\n"

Int(true)             //1

print(NSNumber(value: p1))   

Mayan

Answer 9

In swift 5:

you can do this:

let x = ("a" == "a")

Int(truncating: x as NSNumber)

Schist

Answer 10

This is my preferred adaptation of existing solutions, just an overload of Int. This way I don't have to remember any additional syntax.

func Int(_ boolean: Bool) -> Int {
    boolean ? 1 : 0
}

Biliary