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

[Chris Eidhof]

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()

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`?

-- 
Chris Eidhof
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