What does <<-CONSTANT do?

问题

return <<-HTML
  <li>
    <a href = \"some-link\">Link-Title</a>
  </li>
HTML

What are <<-HTML on the first line and HTML on the last line for?

回答1:

It's a heredoc.

http://en.wikipedia.org/wiki/Here_document#Ruby

回答2:

That's a here document. Basically, it's a multi-line string literal.

On lines after the line with the <<-HTML, those are literal strings concatenated by newlines-- until the end marker is reached, which in this case is HTML.

回答3:

To explicitly answer the question, this snippet returns the string:

<li>

<a href = "some-link">Link-Title</a>

</li>

来源：https://stackoverflow.com/questions/4608902/what-does-constant-do