PHP Anonymous functions: undefined variable

Question

I'm having these two WordPress functions:

$wpb_set_post_views = function($postID) {
    $count_key = 'wpb_post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        $count = 0;
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
    }else{
        $count++;
        update_post_meta($postID, $count_key, $count);
    }
};

add_action( 'wp_head', function ($post_id) {
    if ( !is_single() ) return;
    if ( empty ( $post_id) ) {
        global $post;
        $post_id = $post->ID;
    }
    $wpb_set_post_views($post_id);
});

But the page return Notice: Undefined variable: wpb_set_post_views for the last line.

After function ($post_id) you need to add use (wpb_set_post_views). The variable is out of scope. — Andrei
– Andrei, Commented Sep 7, 2015 at 14:48

Zarathuztra · Accepted Answer · 2015-09-07 14:51:52Z

10

When dealing with Closures in PHP you need to ensure that any out of scope variable is put into the Closure scope. This is unlike JavaScript where closures have access to variables declared in a PHP scope.

Your anonymous function should be as follows

function() use ($variableNeeded) { }

You will then have access to that variable.

It is important to keep in mind that this is a pass by value scenario, so any changes to that variable will not be reflected outside the closure, so you would need to pass by reference to make changes.

function() use (&$variableNeeded) { }

answered Sep 7, 2015 at 14:51

Zarathuztra

3,2411 gold badge23 silver badges34 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Andrei Over a year ago

There's really no need to pass it in by reference.

Zarathuztra Over a year ago

In this example, maybe not, but if you need the value change to be reflected outside the closure, you need to pass by reference. Calling closures is the same as calling any other function, so you will pass by value.

user3535945 · Accepted Answer · 2015-09-07 14:55:53Z

Use global keyword to access the outside variables in a function.

So your code will be

add_action( 'wp_head', function ($post_id) {
    if ( !is_single() ) return;
    if ( empty ( $post_id) ) {
        global $post;
        $post_id = $post->ID;
    }
    global $wpb_set_post_views;
    $wpb_set_post_views($post_id);
});

Or

add_action( 'wp_head', function ($post_id) {
        if ( !is_single() ) return;
        if ( empty ( $post_id) ) {
            global $post;
            $post_id = $post->ID;
        }
        $wpb_set_post_views = $GLOBALS['wpb_set_post_views'];
        $wpb_set_post_views($post_id);
    });

Please refer http://php.net/manual/en/language.variables.scope.php

Collectives™ on Stack Overflow

PHP Anonymous functions: undefined variable

2 Answers 2

2 Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Linked

Related