title: How do go's len() and make() functions work?
body: <p>How do go's <code>len()</code> and <code>make()</code> functions work? Since the language lacks support for both generics and function overloading I don't see how <code>func len(v Type) int</code> is possible. The same goes for <code>func make(Type, size IntegerType) Type</code>.</p>
  
  <p>I can't seem to find the function in the go source, the closest I've managed to find is <a href="https://golang.org/src/builtin/builtin.go" rel="noreferrer">this</a></p>