SwiftUI: How to use `!` operator before `$` bindable object operator?

Question

I'm unable to use logical not ! operator with Bindable $ object.

Here is the scenario I want-

struct ContentView: View {
@State private var isLoggedIn:Bool = true
var body: some View {

    Text("Root View")
        .sheet(isPresented: !self.$isLoggedIn) {
            SignInView()
        }
        .onAppear { self.performAuthentication() }
   }
}

Sign In View should present as soon as I set isLoggedIn = false by some button action. For which I have to use logical not operator before $.

Compiler error: Cannot convert value of type 'Binding' to expected argument type 'Bool'

How can I achieve this?

it is worth to mention that '$' in not 'bindable object operator'. If you have @somePropertyWrapper var value:Value = ..., $ prefix operator gives you its projectedValue. You can get a binding from a State by accessing its binding property. You can also use the $ prefix operator with any property of a State to create a binding. — user3441734
– user3441734, Commented Feb 5, 2020 at 17:12

Martijn Pieters · Accepted Answer · 2022-08-23 14:47:40Z

6

As I said in comment to question there were approach posted for SwiftUI: transform Binding into another Binding. If you, however, want to have it explicitly as operator, you can use the following (tested & works with Xcode 11.2)

extension Binding where Value == Bool {
    static prefix func !(_ lhs: Binding<Bool>) -> Binding<Bool> {
        return Binding<Bool>(get:{ !lhs.wrappedValue }, 
                             set: { lhs.wrappedValue = !$0})
    }
}

edited Aug 23, 2022 at 14:47

Martijn Pieters

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answered Feb 5, 2020 at 14:53

Asperi

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7 Comments

user3441734 Over a year ago

redefining ! operator woks, but i don't think it is good idea. you are better to avoid such a solution ...

matt Over a year ago

@user3441734 Why? It's a great idea (I like this even better than the earlier negate method).

user3441734 Over a year ago

@matt it works, for sure. but without seeing its definition, it could be little bit unclear, especially the set part. !someBool generally don't change the value. it was a nice discussion about someInt++ a year ago, and !someBindigToBool looks for me more "unpredictable"

matt Over a year ago

@user3441734 That's a fair point! You're saying that the advantage of negate is that it can be clearer that it produces a new binding. In fact one might argue just the opposite of what I just said, and suggest that we call that method negativeBinding or similar to make absolutely clear what it does.

user3441734 Over a year ago

@matt .-) yes. let say ! operator is prefix operator which return negated value, but don't change original value. that is what i will expect ... even negativeBinding sounds strange, maybe bindingNegativeValue sounds better.

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