title: How to use "copy" property in Objective-C?
body: <p>I have read through many materials online which all explain when people should use "<code>copy</code>" instead of "<code>strong</code>".</p>
  
  <p>"The copy attribute is an alternative to strong. Instead of taking ownership of the existing object, it creates a copy of whatever you assign to the property, then takes ownership of that. Only objects that conform to the <code>NSCopying</code> protocol can use this attribute..."</p>
  
  <p>And there are plenty of example codes showing when using "copy", the original value stays the same.</p>
  
  <p>However, I'm new to <code>Objective-C</code>. I really want to know how to use the newly assigned value. Where is the "new instance(copy)" with the "new value"? Do I need any additional methods to change the original value if I want to?</p>
  
  <p>It will be great if someone can share an example for this part not the one proving the original value is not changed, which is everywhere.</p>