Remove unnecessary copy-by-reference in do_action()

[scribu]

There's this weird check in do_action():

	if ( is_array($arg) && 1 == count($arg) && isset($arg[0]) && is_object($arg[0]) ) // array(&$this)
		$args[] =& $arg[0];

It was introduced in [4177], probably to fix PHP4 nastiness.

But, since we're on PHP5 now, the copy-by-reference is not needed anymore.

[scribu]

It basically transformed:

array( array( &$this ), 'foo' )

into

array( &$this, 'foo' )

for the callback hooked to that action.

conservative.17111.diff​ simply removes the reference.

17111.diff​ removes the check entirely. Reasons:

• not a useful behaviour anymore
• WP core doesn't use it anywhere; instead, it uses the more flexible do_action_ref_array()
• unlikely that plugins call do_action( 'whatever', array( &$this ) );
• speed improvement

[Denis-de-Bernardy]

unlikely that plugins call do_action( 'whatever', array( &$this ) );

If memory serves, that unlikely call used to be an documented best practice a few years back.

[scribu]

Link, or it didn't happen. :)

[ericmann]

I've seen do_action( 'whatever', &$this ); but not do_action( 'something', array( &$this ) );:

If a plugin somewhere does pass array( &$this ), how bad would things break?

[Denis-de-Bernardy]

Replying to scribu:

Link, or it didn't happen. :)

Sorry, not in much of a drive to google.com/archive.org the reference. FWIW, though, I vaguely recall seeing as an example of good things to do in the codex somewhere between 2005 and 2006. Plus, in case memory serves me wrong, that was the only means of getting the expected behavior (with php4 objects) back then anyway.

I'm arguably biased in some sense, since my own plugins called things that way back then. (Those versions are completely obsolete, so I don't care much; but pointing out why I'm raising the issue.)

This probably may no longer be a necessity with php5 objects (since that is what the array with a reference was all about)... But the rational behind the original behavior shouldn't be forgotten. And I dare suggest that a few test cases might be needed before things do change.

[scribu]

The reason I'm skeptical is because do_action_ref_array() was also introduced in WP 2.1, when this change was made.

Eric & Denis: for a simple testcase, see test-do-action.php​.

[jane]

Not in by freeze, punting.

[scribu]

Not worth the potential back-compat headaches.