How to convert Swift Bool? -> String?

Question

Given a Bool?, I'd like to be able to do this:

let a = BoolToString(optbool) ?? "<None>"

which would either give me "true", "false", or "<None>".

Is there a built-in for BoolToString?

And you would want the true, false, and to be strings? – dannybess Nov 22 '15 at 22:02 — dannybess, Nov 22 '15 at 22:02

score 74 · Answer 1 · answered Jul 20 '16 at 21:46

74

String(Bool) is the easiest way.

var myBool = true
var boolAsString = String(myBool)

answered Jul 20 '16 at 21:46

Random Swift User

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user3441734 · Accepted Answer · 2015-11-22T22:48:11.843

60

let b1: Bool? = true
let b2: Bool? = false
let b3: Bool? = nil

print(b1?.description ?? "none") // "true"
print(b2?.description ?? "none") // "false"
print(b3?.description ?? "none") // "none"

or you can define 'one liner' which works with both Bool and Bool? as a function

func BoolToString(b: Bool?)->String { return b?.description ?? "<None>"}

edited Nov 22 '15 at 22:48

answered Nov 22 '15 at 22:24

user3441734

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Change `"none"` to `""`. I think we have a winner here! :-) – vacawama Nov 22 '15 at 22:27
That's not quite orthodox Swift programming, the conventions of conversion via type initializers is one of prominent feature of all data conversion APIs. However, `CustomStringConvertible`, which declares `description` is an API that semantically is supposed to be used not for data serialization but debugging purposes. You should always use String.init(_:) instead. – Isaaс Weisberg Aug 09 '21 at 13:02
@IsaaсWeisberg is certainly right. The documentation for `description` discourages calling it directly. https://developer.apple.com/documentation/swift/customstringconvertible – Patrick Feb 14 '22 at 15:01

Elijah · Answer 3 · 2018-03-30T02:52:57.167

24

let trueString = String(true) //"true"
let trueBool = Bool("true")   //true
let falseBool = Bool("false") //false
let nilBool = Bool("foo")     //nil

edited Mar 30 '18 at 02:52

answered Dec 18 '17 at 05:14

Elijah

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This is perfect. Thanks! – Baran Apr 01 '19 at 14:43

vacawama · Answer 4 · 2015-11-23T04:31:41.463

You could use the ?: ternary operator:

let a = optBool == nil ? "<None>" : "\(optBool!)"

Or you could use map:

let a = optBool.map { "\($0)" } ?? "<None>"

Of the two, optBool.map { "\($0)" } does exactly what you want BoolToString to do; it returns a String? that is Optional(true), Optional(false), or nil. Then the nil coalescing operator ?? unwraps that or replaces nil with "<None>".

Update:

This can also be written as:

let a = optBool.map(String.init) ?? "<None>"

or:

let a = optBool.map { String($0) } ?? "<None>"

TotoroTotoro · Answer 5 · 2016-12-24T17:37:04.730

4

var boolValue: Bool? = nil
var stringValue = "\(boolValue)" // can be either "true", "false", or "nil"

Or a more verbose custom function:

func boolToString(value: Bool?) -> String {
    if let value = value {
        return "\(value)"
    }
    else { 
        return "<None>"
        // or you may return nil here. The return type would have to be String? in that case.
    }

}

edited Dec 24 '16 at 17:37

answered Nov 22 '15 at 22:03

TotoroTotoro

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So, no? There is no built-in way? – Nov 22 '15 at 22:05
This defers to CustomStringConvertible i.e. the same solution as accepted answer. – Isaaс Weisberg Aug 09 '21 at 13:05

score 0 · Answer 6 · answered Aug 08 '20 at 09:52

You can do it with extensions!

extension Optional where Wrapped == Bool {
  func toString(_ nilString: String = "nil") -> String {
    self.map { String($0) } ?? nilString
  }
}

Usage:

let b1: Bool? = true
let b2: Bool? = false
let b3: Bool? = nil

b1.toString() // "true"
b2.toString() // "false"

b3.toString() // "nil"
b3.toString("<None>") // "<None>"

How to convert Swift Bool? -> String?

6 Answers6