Four variations of jQuery ready() -- what's the difference?

Question

I've seen four different ways to tell jQuery to execute a function when the document is ready. Are these all equivalent?

$(document).ready(function () {
  alert('$(document).ready()');
});  

$().ready(function () {
  alert('$().ready()');
}); 

$(function () {
  alert('$()');
});     

jQuery(function ($) {
  alert('jQuery()');
});

Answer 1

There is no difference.

$ is the same as jQuery. If you view the unminified source, you will see var $ = jQuery = ... or something to that effect.

The jQuery function checks the type of it's parameter, if it is a function, it treats it the same as $(document).ready(...)

Calling jQuery without a parameter defaults to using document. So $() and $(document) are identical. Try it in Firebug.

Answer 2

re: Geroge IV's comments regarding $() == $(document) its correct. From the unminified source (init is what get called internally):

init: function( selector, context ) {
 // Make sure that a selection was provided
 selector = selector || document;

Also from source, to back up previous conversations:

// HANDLE: $(function)
 // Shortcut for document ready
 } else if ( jQuery.isFunction( selector ) )
  return jQuery( document ).ready( selector );

this should be community wiki. I've always been interested in the inner workings of jquery, now I've had an excuse to start looking :-)