title: Immutable value of type [Card] only has mutating values of name append
body: <p>I have a Card class and a Player class. </p>
  
  <p>In my Player class I have a function that takes a [Card] array and adds a Card to it.</p>
  
  <p>However, when I call...</p>
  
  <pre><code>myCardArray.append(myCard)
  </code></pre>
  
  <p>...I get the error</p>
  
  <pre><code>Immutable value of type [Card] only has mutating values of name append
  </code></pre>
  
  <p>I can't figure out why this is? Why would this be immutable?</p>