title: What's the difference between `alias` and `typedef`?
body: <p>All this time I've been using <code>alias</code>, but today I discovered by chance that D has <code>typedef</code>.  Interesting enough, TDPL doesn't even cover it as far as I can tell (not even listed in <code>D Keywords</code> nor the Errata).  The <a href="http://www.d-programming-language.org/cpptod.html#typedefs" rel="noreferrer">site does cover it</a>, but it doesn't talk about it much.  My code compiles with either, but what is the difference between the two, and when should I use <code>typedef</code> over <code>alias</code>?</p>