SwiftUI TextField won't change its contents under weird corner case with Binding<String> computed property

I have a TextField inside a SwiftUI body. I have bound it to a @State var through an intermediary binding which lets me get and set a computed value...

struct ExampleView: View {

@State var symbolToBeValidated: String = ""

var body: some View {
    let binding = Binding<String> (get: {
        return self.symbolToBeValidated
    }, set: {
        var newString = $0.uppercased()
        self.symbolToBeValidated = newString // <- fig. 1: redundant assignment I wish I didn't have to put

        newString = newString.replacingOccurrences(
            of: #"[^A-Z]"#,
            with: "",
            options: .regularExpression
        )
        
        self.symbolToBeValidated = newString // <- fig. 2: the final, truly valid assignment
    })
    
    let form = Form {
         Text("What symbol do you wish to analyze?")
         TextField("ex.AAPL", text: binding)
// [...]

I'm using the intermediary Binding so that I can transform the string to always be an Uppercased format only containing letters A-Z (as referenced by my .regularExpression). (I'm trying to make it so that the TextField only shows a validly formatted Stock Symbol on each keypress).

This works, somewhat. The problem I discovered is that if I don't call the assignment twice (as seen in fig 1) the TextField will begin to show numbers and letters (even though it isn't included in the symbolToBeValidated string. This happens, I suspect, because SwiftUI is checking the oldValue against the newValue internally, and because it hasn't changed in the background, it doesn't call a refresh to get the internal value again. The way I've found to thwart this is to include an extra assignment before the .replacingOccurences call.

This results in the number or symbol being flashed on the screen for a blip as it is being typed by the user, then it is correctly removed by the .replacingOccurences call.

There must be a more elegant way to do this. I went down the Formatter class type and tried this alternative only because Formatter resulted in a similar behavior where the errant character would blip on the screen before being removed.

If someone knows a way for this to be intercepted before anything is displayed on the screen, I would appreciate it. This is super nit-picky, but I'm just fishing for the right answer here.

Try this:

extension Binding where Value == String {
    public func validated() -> Self {
        return .init(
            get: { self.wrappedValue },
            set: {
                var newString = $0.uppercased()
                newString = newString.replacingOccurrences(
                    of: #"[^A-Z]"#,
                    with: "",
                    options: .regularExpression
                )
                self.wrappedValue = newString
            }
        )
    }
}

// ...

TextField("ex.AAPL", text: self.$symbolToBeValidated.validated())

This way also allows you to reuse and test the validation code.