What does extract( shortcode_atts( array( do?

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The codex says

shortcode_atts() combines user shortcode attributes with known attributes and fills in defaults when needed. The result will contain every key from the known attributes, merged with values from shortcode attributes.

It doesn’t make much sense to me (I’m a newbie).

Here is an example:

function wps_trend($atts) {
    extract( shortcode_atts( array(
        'w' => '500', 
        'h' => '330',
        'q' => '',
        'geo' => 'US',
    ), $atts));
    $h = (int) $h;
    $w = (int) $w;
    $q = esc_attr($geo);
    ob_start();

Please can you explain?

1

shortcode_atts() works like array_merge(): It merges the second list of arguments into the first one. The difference is: It merges only keys present in the first argument ($default).

extract() then takes the array keys, sets these as variable names and their values as variable values. 'w' => '500' in your example becomes $w = '500'.

Do not use extract(). This very bad code style. Its usage was deprecated even in core, and that means something … 🙂

Your example should be written as:

$args = shortcode_atts( 
    array(
        'w'   => '500',
        'h'   => '330',
        'q'   => '',
        'geo' => 'US',
    ), 
    $atts
);
$w = (int) $args['w'];
$h = (int) $args['h'];
$q = esc_attr( $args['q'] );

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