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

[Adrian Zubarev]

The trues is that `isTrue` doesn’t really make sense because boolean instances are named in a way where `isTrue` is rendered redundant.


Am 13. Januar 2018 um 20:09:41, C. Keith Ray via swift-evolution (swift-evolution at swift.org) schrieb:

If you would like something better than "== false" I suggest adding computed properties 'isTrue' and 'isFalse' to Boolean.


On Jan 13, 2018, at 11:06 AM, Karl Wagner via swift-evolution <swift-evolution at swift.org> wrote:



On 12. Jan 2018, at 20:54, 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


Yeah so do I. ! is a very narrow character and totally changes the meaning of the logic.

That said, I can’t come up with a clearer name than “== false”. inverted() isn’t helpful. toggle() on a mutable Bool is good, though.

- Karl

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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-- 
Alejandro Martinez
http://alejandromp.com
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