title: What does the dollar sign do in Swift / SwiftUI?
body: <p><a href="https://developer.apple.com/tutorials/swiftui/handling-user-input" rel="noreferrer">This tutorial by Apple about SwiftUI</a> uses a dollar sign to bind data, and I‘m having trouble finding more information about this data binding in SwiftUI.</p>
  
  <pre><code>Toggle(isOn: $showFavoritesOnly) {
  </code></pre>
  
  <blockquote>
    <p>You use the $ prefix to access a binding to a state variable, or one of its properties.</p>
  </blockquote>
  
  <p>Is this some sort of <code>inout</code> type parameter? That uses the ampersand to pass it on.</p>