Errors:
For the majority of WordPress users, the use of is_a in the core files is of little concern. The E_STRICT errors, in PHP versions >= 5.0 < 5.3 only, can be safely ignored and are not a problem if error reporting does not include them.
Performance:
For those that have PHP versions >= 5.0 and desire a slight improvement in performance, changing the code to use the instanceof operator, at least in the wp-includes/classes.php file, may be worth the effort. In my crude tests is_a ran in .000023 seconds and instanceof in .0000082 seconds. As the is_wp_error() function is called hundreds of times per page load, this one edit will amount to a saving of roughly .0074 seconds per page load.
Readability:
The use of either is_a or instanceof in conditional tests is readable and it is easy to comprehend the intent. My use of get_class and is_subclass_of, although supported in all versions of PHP, not so much.
Maintainability:
Considering how often new versions of WordPress are released — 2 more in the short time since this series of posts began — making 38 edits in 15 files just to replace the use of is_a with something else could become a chore.
To summarize, several things need to be considered before making any edits to the WordPress core files:
- Are the E_STRICT errors important?
- What version of PHP is the server running?
- How important is performance?
- How important is code readability?
- How important is maintainability?
Technique PHP Speed Errors Readability is_a 4,5 slow Strict* simple instanceof 5 fast $var fix** simple get_class is_subclass_of 4,5 mid*** $var fix** complex
* is_a is only an E_STRICT error for PHP versions >= 5.0 < 5.3
** Both instanceof and is_subclass_of can cause fatal errors in PHP versions 5.0 < 5.1 unless a work-around is used, in my examples, by using a variable to hold the class name.
*** When get_class alone is enough, the conditional approximates the speed of instanceof, but when PHP must test for is_subclass_of the speed is closer to, but a bit faster than, that of is_a
Choices for is a:
is_a($object, 'WP_Class')
( $object instanceof WP_Class )
$class_name = 'WP_Class';
( $object instanceof $class_name )
( ( get_class($object) == 'WP_Class' )
|| is_subclass_of($object, 'WP_Class') )
$class_name = 'WP_Class';
( ( get_class($object) == 'WP_Class' )
|| is_subclass_of($object, $class_name) )Choices for Not is a:
!is_a($object, 'WP_Class')
!( $object instanceof WP_Class )
$class_name = 'WP_Class';
!( $object instanceof $class_name )
( ( get_class($object) != 'WP_Class' )
&& !is_subclass_of($object, 'WP_Class') )
$class_name = 'WP_Class';
( ( get_class($object) != 'WP_Class' )
&& !is_subclass_of($object, $class_name) )WordPress core files containing is_a
- wp-includes/category-template.php
- wp-includes/classes.php
- wp-includes/class-feed.php
- wp-includes/class-IXR.php
- wp-includes/class-simplepie.php
- wp-includes/functions.wp-scripts.php
- wp-includes/functions.wp-styles.php
- wp-includes/general-template.php
- wp-includes/pluggable.php
- wp-includes/script-loader.php
- wp-includes/user.php
- wp-includes/widgets.php
- wp-includes/Text/Diff.php
- wp-includes/Text/Diff/Renderer.php
- wp-admin/includes/template.php
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