do_action default first parameter

[Tkama]

This code looks like bug: we don't pass any parameters to action but the first parameter is passed anyway and have the value (empty string). Why?

<?php
add_action( 'action_name', function( $first ){
        var_dump( $first );
} );

do_action( 'action_name' ); //> string(0) ""

[donmhico]

Hi @Tkama,

Navigating the codebase, seems like this line is responsible - https://core.trac.wordpress.org/browser/trunk/src/wp-includes/plugin.php#L472

While it's just easy to remove the if clause, i'm not sure if it won't introduce any compatibility issues.

[Tkama]

@donmhico thanks. There is no difficulties to find the reason and fix it for me. The idea of this ticket: maybe it's better to fix core code for more predictable behavior of such code.

For example:

<?php
add_action( 'action_name', function( $first = 'foo' ){
     // some logic

     echo $first
} );

do_action( 'action_name' );

As we can see. We don't pass any params to

do_action( 'action_name' );

and we expect the code print foo but not ''.

Such hook-call logic we can use, for example, for plugins when we want wrap some plugin function, for save plugin deactivation when plugin function is used inside the theme template files.