Where does $data come from?

[s22-tech]

In the following example from https://github.com/SosthenG/yourls-notifier/, what is $data populated with and where does it come from? It seems to be pulled out of thin air. 😁

yourls_add_filter('add_new_link', 'notify_new_link');
function notify_new_link($data) {
	...
}

Knowing how this works will help a lot in writing my own plugins.

Thanks,
Marc

[dgw]

It comes from the filter pipeline:

YOURLS/includes/functions-shorturls.php

Line 162 in a3cdf42

return yourls_apply_filter( 'add_new_link', $return, $url, $keyword, $title );

$return is the first filter parameter, and becomes what that plugin calls $data when the filter's arguments are generated (by inspecting how many parameters the filter function expects):

YOURLS/includes/functions-plugins.php

Lines 224 to 237 in a3cdf42

	foreach ( (array)current( $yourls_filters[ $hook ] ) as $the_ ) {
	if ( !is_null($the_[ 'function' ]) ) {
	$args[ 1 ] = $value;
	$count = $the_[ 'accepted_args' ];
	if ( is_null( $count ) ) {
	$_value = call_user_func_array( $the_[ 'function' ], array_slice( $args, 1 ) );
	}
	else {
	$_value = call_user_func_array( $the_[ 'function' ], array_slice( $args, 1, (int)$count ) );
	}
	}
	if ( $the_[ 'type' ] == 'filter' ) {
	$value = $_value;
	}

Finally, the PHP docs for call_user_func_array():

call_user_func_array(callable $callback, array $args):

Calls the callback given by the first parameter with the parameters in args.

[ozh]

See tutorial : https://github.com/YOURLS/YOURLS/wiki/How-to-make-Plugins