In a view, how can I change the view's variables every time I press a button, using a struct's function?

I have a problem while coding in content view. I don’t understand how can I use struct’s func in content view. I would like to get helps from you guys. I get an error like this "Result of call to ‘changeText(text:)’ is unused".

Here’s simple example of what I’m trying to achieve,

import Foundation

public struct Brain {

  public func changeText(text: String) -> String{
    var text = text
    text = "Changed text!"
    return text
  }
}

import SwiftUI

struct ContentView: View {
  @State var tmp: String = "hello"
  var tmpTwo: Brain = Brain()
    var body: some View {
        VStack {
          Button(action: {
            tmpTwo.changeText(text: tmp )
          }, label: {
            Text(tmp)
          })

        }
        .padding()
    }
}

>Solution :

You need to use the return value of the function like so:

import SwiftUI

struct ContentView: View {
  @State var tmp: String = "hello"
  var tmpTwo: Brain = Brain()
    var body: some View {
        VStack {
          Button(action: {
            tmp = tmpTwo.changeText(text: tmp )
          }, label: {
            Text(tmp)
          })
        }
        .padding()
    }
}