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

Developer Documentation

Developer documentation can be found in DEVELOPER-DOCS.md. That documentation covers the template tags and hooks provided by the plugin.

As an overview, these are the template tags provided by the plugin:

• _sfc() : Safely call a function and get its return value.
• _sfce() : Safely call a function and echo its sanitized 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).

These are the hooks provided by the plugin. They 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.

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