[swift-evolution] [pitch] adding toggle to Bool

[Anders Kierulf]

I also avoid using ! for negation when possible, and `toggle` or `invert` will be helpful, but in many cases I think the negative case is better expressed directly. For example, I find that using `nonEmpty` instead of !isEmpty makes the code easier to read: 

  extension String {
      var nonEmpty: Bool { return !self.isEmpty }
  }

  if !string.isEmpty { … }

  if string.isEmpty.inverted() { … }

  if string.nonEmpty { … }

For the case of `contains`, maybe define `lacks`?

  if !items.contains(item) { ... }

  if items.contains(item).inverted() { ... }

  if items.lacks(item) { ... }

Anders Kierulf

> On Jan 12, 2018, at 12:54 PM, Alejandro Martinez via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I wouldn't go as far as to ask to fade out ! but in all my code I end
> up doing == false just for readability. That ! knows who to hide
> himself too well :P
> 
> On Fri, Jan 12, 2018 at 10:13 AM, Adrian Zubarev via swift-evolution
> <swift-evolution at swift.org> wrote:
>> I’m not sure if this would be considered or not, but I would like if the
>> negation operator `!` would fade out.
>> 
>> If this is ever going to a review then I’d suggest that we add a pair of
>> functions, one mutating and the other non-mutating.
>> 
>> extension Bool {
>>  mutating func invert() {
>>    self = !self
>>  }
>> 
>>  func inverted() {
>>    return !self
>>  }
>> }
>> 
>> I’d rather use `inverted` instead of `!` because of the readability this
>> function provides.
>> 
>> if !items.contains(item) { ... }
>> 
>> if items.contains(item).inverted() { ... }
>> 
>> ——
>> 
>> I personally have some other extensions like:
>> 
>> extension Bool {
>>  @discardableResult
>>  func whenTrue<T>(execute closure: () throws -> T) rethrows -> T? {
>>    if self { return try closure() }
>>    return nil
>>  }
>> 
>>  @discardableResult
>>  func whenFalse<T>(execute closure: () throws -> T) rethrows -> T? {
>>    if !self { return try closure() }
>>    return nil
>>  }
>> }
>> 
>> But this is more a personal preference.
>> 
>> ——
>> 
>> That said, if the community is fine with the `invert/inverted` pair then I’d
>> say go for it ;)
>> 
>> Am 12. Januar 2018 um 09:14:22, Nate Cook via swift-evolution
>> (swift-evolution at swift.org) schrieb:
>> 
>> 
>> On Jan 12, 2018, at 12:15 AM, Chris Eidhof via swift-evolution
>> <swift-evolution at swift.org> wrote:
>> 
>> Hey SE!
>> 
>> When we have a bunch of nested structs:
>> 
>>    struct Sample {
>>        var bar: Bar
>>    }
>> 
>>    struct Bar {
>>        var show: Bool
>>    }
>> 
>>    var foo = Sample(bar: Bar(show: false))
>> 
>> It can be repetitive to toggle a deeply nested boolean:
>> 
>>    foo.bar.show = !foo.bar.show // duplication
>> 
>> I sometimes add a `toggle` extension on `Bool`
>> 
>>    extension Bool {
>>        mutating func toggle() {
>>            self = !self
>>        }
>>    }
>> 
>> This allows you to write the same code without duplication, and makes the
>> intent clearer:
>> 
>>    foo.bar.show.toggle()
>> 
>> 
>> I like it!
>> 
>> In other languages, I don't think the `toggle` would make as much sense, but
>> the mutable self makes this very useful.
>> 
>> After I posted it on Twitter, it turns out I'm not the only one:
>> https://twitter.com/PublicExtension/status/730434956376346624
>> 
>> I would have gone straight to a proposal, but I think we can do some
>> bikeshedding about the name of `toggle`?
>> 
>> 
>> Another verb that could work is `invert`.
>> 
>> The `!` operator that does this is the negation operator, but I think
>> `negate` could sound to some like "make this false" rather than toggling.
>> 
>> Nate
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>> 
>> 
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> 
> 
> 
> -- 
> Alejandro Martinez
> http://alejandromp.com
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