Safe Function Call

Description

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 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).

Theses 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.

Installation

  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

FAQ

Do the functions provided by this plugin capture any error messages generated by the specified function?

No.

Why would I use any of these functions instead of using `function_exists()`/`method_exists()` directly?

The functions provided by this plugin provide a more concise syntax for checking for function existence (but they do use function_exists()/method_exists() under the hood). _sfce() will both echo and return the echoed value, which may be of use in certain circumstances. And also, since the callback to be safely called is passed as an argument, it can be easily and more concisely parameterized.

Won’t the problems this plugin addresses become a problem when using this plugin if it itself gets deactivated?

Yes, if you make direct use of one of this plugin’s functions and then deactivate the plugin, you will likely encounter an error.

However, if you make use indirect filter invocation, you can prevent errors. See the “Filter invocation method” section of the extended plugin description for example code.

Does this plugin include unit tests?

Yes.

Reviews

januar 11, 2017
Works perfectly and offers enough fallback context to be very useful in theme development, especially themes or plugins which are designed for developers to extend. Thank you.
Read all 1 review

Contributors & Developers

“Safe Function Call” is open source software. The following people have contributed to this plugin.

Contributors

Translate “Safe Function Call” into your language.

Interested in development?

Browse the code, check out the SVN repository, or subscribe to the development log by RSS.

Changelog

1.3.2 (2023-05-19)

  • New: Add DEVELOPER-DOCS.md and move hooks documentation into it
  • New: Add TODO.md with potential TODO items
  • Change: Improve some inline documentation formatting
  • Change: Note compatibility through WP 6.3+
  • Change: Update copyright date (2023)

1.3.1 (2021-09-26)

  • Change: Note compatibility through WP 5.8+
  • Unit tests:
    • Change: Restructure unit test directories
      • Change: Move phpunit/bin/ into tests/
      • Change: Move phpunit/ into tests/
    • Change: Remove ‘test-‘ prefix from unit test file
    • Change: In bootstrap, store path to plugin file constant
    • Change: In bootstrap, add backcompat for PHPUnit pre-v6.0

1.3 (2021-04-17)

Highlights:

  • This minor release adds support for a safer method of invoking the plugin’s own functions in a way that safeguards your usage against errors if the plugin gets deactivated and also notes compatibility through WP 5.7+.

Details:

  • New: Support filter invocation for all functions
    • Add filter _sfc to support filter invocation method _sfc()
    • Add filter _sfce to support filter invocation method _sfce()
    • Add filter _sfcf to support filter invocation method _sfcf()
    • Add filter _sfcm to support filter invocation method _sfcm()
  • Change: Fix incorrect function docblock description and remove repeated word in some parameter docblocks
  • Change: Note compatibility through WP 5.7+
  • Change: Update copyright date (2021)

Full changelog is available in CHANGELOG.md.