Developer Documentation

This plugin provides hooks and template tags.

Template Tags

The plugin provides four template tags for use in your theme templates, functions.php, or plugins.

Functions:

• <?php function _sfc( $callback, ...$params ) ?> This will safely invoke the specified callback. You can specify an arbitrary number of additional arguments that will get passed to it. If the callback does not exist, nothing is displayed and no error is generated.
• <?php function _sfce( $callback, ...$params ) ?> The same as _sfc() except that it echoes the return value of the callback before returning that value.
• <?php function _sfcf( $callback, $fallback_callback = '', ...$params ) ?> The same as _sfc() except that it invokes the fallback callback (if it exists) if the callback does not exist. $function_name_if_missing() is sent $function_name as its first argument, and then subsequently all arguments that would have otherwise been sent to $function_name().
• <?php function _sfcm( $callback, $message_if_missing = '', ...$params ) ?> The same as _sfc() except that it displays a message (the value of $message_if_missing), if the callback does not exist.

Arguments:

• $callback (string) A string representing the name of the function to be called, or an array of a class or object and its method (as can be done for add_action()/add_filter())

• $message_if_missing (string) (For _sfcm() only.) The message to be displayed if $function_name() does not exist as a function.

• $fallback_callback (string) (For _sfcf() only.) The function to be called if the callback does not exist.

• $params (mixed) After their explicitly listed arguments, all functions accept any number of additional arguments, all of which will be passed to the callback as parameters.

Examples:

• Calling list_cities(), a valid function: <?php _sfc('list_cities', 'Texas', 3); ?> => "Austin, Dallas, Fort Worth"

• Calling list_cities(), a valid method in the existing class Cities: <?php _sfc(array('Cities', 'list_cities'), 'Texas', 3); ?> => "Austin, Dallas, Fort Worth"

• Calling list_cities(), a valid method of the $obj object, which is also valid: <?php _sfc(array($obj, 'list_cities'), 'Texas', 3); ?> => "Austin, Dallas, Fort Worth"

• Calling list_cities(), an invalid function: <?php _sfc('list_cities', 'Texas', 3); ?> => ""

• Calling largest_city(), a valid function that does not echo/display its return value: <?php _sfce('largest_city', 'Tx'); ?> => "Houston"

• Calling list_citites(), a valid function, echoing a message if it doesn't exist: <?php _sfcm('list_cities', 'Unable to list cities at the moment', 'Texas', 3); ?> => "Austin, Dallas, Fort Worth"

• Calling list_cities(), an invalid function, echoing a message if it doesn't exist: <?php _sfcm('list_cities', 'Unable to list cities at the moment', 'Texas', 3); ?> => "Unable to list cities at the moment"

• Calling list_cities(), a valid function, but invoking another callback if it wasn't valid: <?php _sfcf('list_cities', 'unavailable_function_handler', 'Texas', 3); ?> => "Austin, Dallas, Fort Worth"

• Calling list_cities(), an invalid function, but invoking another callback if it wasn't valid: <?php _sfcf('list_cities', 'unavailable_function_handler', 'Texas', 3); ?> => "Sorry, but the function list_cities() does not exist."

	function unavailable_function_handler( $callback ) {
		echo "Sorry, but the function {$callback}() does not exist.";
	}

Hooks

The plugin exposes a number of filters for hooking. Code using these filters should ideally be put into a mu-plugin or site-specific plugin (which is beyond the scope of this readme to explain). These hooks are intended for filter invocation usage rather than typical content filtering.

• _sfc : Filter to safely invoke _sfc() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.
• _sfce : Filter to safely invoke _sfce() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.
• _sfcf : Filter to safely invoke _sfcf() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.
• _sfcm : Filter to safely invoke _sfcm() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.

_sfc (filter)

The _sfc hook allows you to use an alternative approach to safely invoke _sfc() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.

Arguments:

• same as for _sfc()

Example:

Instead of:

<?php $cities = _sfc( 'list_cities', 'Texas', 3 ); ?>

Do:

<?php $cities = apply_filters( '_sfc', 'list_cities', 'Texas', 3 ); ?>

_sfce(filter)

The _sfce hook allows you to use an alternative approach to safely invoke _sfce() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.

Arguments:

• same as for _sfce()

Example:

Instead of:

<?php _sfce( 'largest_city', 'Tx' ); ?>

Do:

<?php apply_filters( '_sfce', 'largest_city', 'Tx' ); ?>

_sfcf(filter)

The _sfcf hook allows you to use an alternative approach to safely invoke _sfcf() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.

Arguments:

• same as for _sfcf()

Example:

Instead of:

<?php _sfcf( 'nonexistent_function', 'unavailable_function_handler' ); ?>

Do:

<?php apply_filters( '_sfcf', 'nonexistent_function', 'unavailable_function_handler' ); ?>

_sfcm(filter)

The _sfcm hook allows you to use an alternative approach to safely invoke _sfcm() in such a way that if the plugin were deactivated or deleted, then your calls to the function won't cause errors in your site.

Arguments:

• same as for _sfcm()

Example:

Instead of:

<?php _sfcm( 'list_cities', 'Unable to list cities at the moment', 'Texas', 3 ); ?>

Do:

<?php apply_filters( '_sfcm', 'list_cities', 'Unable to list cities at the moment', 'Texas', 3 ); ?>