title: What is +++ and <<< on Swift?
body: <p>I just know from this <a href="https://github.com/xmartlabs/Eureka#usage" rel="noreferrer">github project</a> that Swift has <code>+++</code> and <code>&lt;&lt;&lt;</code> "operators". </p>
  
  <p>It's hard for me to search for this on google because <code>+++</code> and <code>&lt;&lt;&lt;</code> maybe some kind of special characters and not showing up on search result at all. It's not even showing up on <strong>questions that may already have your answer</strong> section of Stack Overflow when I wrote the question title. </p>
  
  <p>Can you explain briefly what are these weird operators for, and maybe some articles link for further reading?</p>