Safe Function Call

Safely call a function, class method, or object method in a manner that doesn’t generate errors if those plugins cease to exist.

Various helper functions are provided that provide handy variations of this theme:

• _sfc(): Safely call a function and get its return value
• _sfce(): Safely call a function and echo its return value
• _sfcf(): Safely call a function; if it doesn’t exist, then a fallback function (if specified) is called
• _sfcm(): Safely call a function; if it doesn’t exist, then echo a message (if provided)

Let’s assume you had something like this in a template:

<?php list_cities( 'Texas', 3 ); ?>

If you deactivated the plugin that provided list_cities(), your site would generate an error when that template is accessed.

You can instead use _sfc(), which is provided by this plugin to call other functions, like so:

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

That will simply do nothing if the list_cities() function is not available.

If you’d rather display a message when the function does not exist, use _sfcm() instead, like so:

<?php _sfcm( 'list_cities', 'The cities listing is temporarily disabled.', 'Texas', 3 ); ?>

In this case, if list_cities() is not available, the text “The cities listing is temporarily disabled.” will be displayed.

If you’d rather call another function when the function does not exist, use _sfcf() instead, like so:

<?php
    function unavailable_function_handler( $function_name ) { echo "The function $function_name is not available."; }
    _sfcf( 'nonexistent_function', 'unavailable_function_handler' );
?>

In the event you want to safely call a function and echo its value, you can use _sfce() like so:

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

Which is roughly equivalent to doing :

<?php if function_exists( 'largest_city' ) { echo largest_city( 'Tx' ); } ?>

Filter invocation method

To further prevent issues in your code should this plugin itself become deactivated, you can use indirect filter invocation to call the plugin functions. Each function has an associated filter with the same name as the function. Simply use apply_filters() to invoke that function instead of calling the function directly.

E.g. instead of:

<?php _sfce( 'some_plugin_function_that_echoes', 'argument' ); ?>

Do:

<?php apply_filters( '_sfce', 'some_plugin_function_that_echoes', 'argument' ); ?>

If you’re relying on the return value of a function and this plugin gets deactivated, note that the apply_filters() call will return the name of the function you intended to call, so you should check the return value to ensure the function got called.

Instead of:

<?php $x = _sfc( 'some_plugin_function', 'argument' ); ?>

Do:

<?php
    $x = apply_filters( '_sfcq', 'some_plugin_function', 'argument' );
    if ( $x !== 'some_plugin_function' ) {
        // Work with the value of $x here.
    } else {
        // The Safe Function Call plugin isn't active.
        $x = 0; // Maybe set the variable to something that makes sense in this scenario.
    }
?>

Links: Plugin Homepage | Plugin Directory Page | GitHub | Author Homepage

Template Tags

The plugin provides four functions for your use. Note: These functions are not limited to use in templates

Functions

• <?php function _sfc($callback) ?>
  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) ?>
  The same as _sfc() except that it echoes the return value of the callback before returning that value.

• <?php function _sfcf($callback, $fallback_callback = '') ?>
  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 = '') ?>
  The same as _sfc() except that it displays a message (the value of $message_if_missing), if the callback does not exist.

Arguments

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

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

Examples

• <?php _sfc('list_cities', 'Texas', 3); /* Assuming list_cities() is a valid function */ ?>
  “Austin, Dallas, Fort Worth”

• <?php _sfc(array('Cities', 'list_cities'), 'Texas', 3); /* Assuming list_cities() is a valid function in the 'Cities' class */ ?>
  “Austin, Dallas, Fort Worth”

• <?php _sfc(array($obj, 'list_cities'), 'Texas', 3); /* Assuming list_cities() is a valid function in the object $obj */ ?>
  “Austin, Dallas, Fort Worth”

• <?php _sfc('list_cities', 'Texas', 3); /* Assuming list_cities() is not a valid function */ ?>
  “”

• <?php _sfcm('list_cities', 'Texas', 'Unable to list cities at the moment', 3); /* Assuming list_cities() is a valid function */ ?>
  “Austin, Dallas, Fort Worth”

• <?php _sfcm('list_cities', 'Texas', 'Unable to list cities at the moment', 3); /* Assuming list_cities() is not a valid function */ ?>
  “Unable to list cities at the moment”

• <?php _sfce('largest_city', 'Tx'); /* Assuming largest_city() is a valid function that does not echo/display its return value */ ?>
  “Houston”

• <?php
function unavailable_function_handler( $callback ) {
echo "Sorry, but the function {$callback}() does not exist.";
}
_sfcf('nonexistent_function', 'unavailable_function_handler');
?>

Find out more at the plugin’s WordPress Plugin Repository page.

1. Install via the built-in WordPress plugin installer. Or download and unzip safe-function-call.zip inside the plugins directory for your site (typically wp-content/plugins/)
2. Activate the plugin through the ‘Plugins’ admin menu in WordPress
3. Use any of the four functions provided by this plugin as desired