Most idiotic problem with assign value to value?

It would be so much easier if you provided simple and complete reproducible code…

So I recreated a simple test code:

enum ResultType {
    case success(formula: Float)
    case failure
}

struct CustomFunction {
    var formula: Float = 0.5
    
    func checkFormula(_ formula: Float) -> ResultType {
        if formula > 0 {
            return .success(formula: formula)
        }
        return .failure
    }
}

struct CustomFormulaView: View {
    @Binding var function: CustomFunction
    @State var testFormula: Float = 0
    
    var body: some View {
        
        HStack {
            Text("    test formula ")
            TextField("", value: $testFormula, format: .number)
        }
        .onChange(of: testFormula) {
            debugPrint("change of test formula: \(testFormula)")
            switch function.checkFormula(testFormula) {
                case .success(let formula):
                    debugPrint("before Change: \(function.formula)")
                    function.formula = formula // Nothing happens
                    debugPrint("Test formula changed: \(testFormula)")
                    debugPrint("set to success: \(formula)")
                    debugPrint("what inside function? \(function.formula)")
                    /*
                     Task {
                     //Generate Image
                     testImage = await function.image(
                     size: testImageSize),
                     simulate: manager.finalSize)
                     break              debugPrint("test image updated for: \(function.formula)")
                     }
                     */
                    
                case .failure :
                    print("failed") ; break
            }
        }
    }
}

struct ContentView: View {
    @State var function = CustomFunction()

    var body: some View {
        CustomFormulaView(function: $function)
        Text("\(function.formula)")
    }
}

And get what I understand is the expected result

"change of test formula: 2.0"
"before Change: 0.5"
"Test formula changed: 2.0"
"set to success: 2.0"
"what inside function? 2.0"

Bindings in superview was defined inside body.

Thanks for the feedback.

Just shows you should post complete code. This would have been obvious and avoided we loos time to search.