为什么这个php函数不执行？

Question

The following is a section of a php document, with a couple of conditionals. The first, if truthy, stores an anonymous function in a variable $the_image_styles, which is successfully called a few lines later. The second, if truthy, store an anonymous function in a variable $the_overlay_styles, which never subsequently executes.

WordPress outputs the following: Call to undefined function the_overlay_styles()

It appears to me there's no difference between the two declarations/invocations, but clearly that's not the case. What am I missing?

<?php
$banner = get_field('banner_image');
// Check for image
if ($banner) :
    $xpos = get_field('banner_xpos');
    $ypos = get_field('banner_ypos');
    // Style string for background image
    $the_image_styles = function() use ($banner, $xpos, $ypos){
        echo "background-image:url({$banner['sizes']['large']}); background-position:{$xpos} {$ypos}";
    };
    // Check for overlay, for later use
    $has_overlay = get_field('has_banner_overlay');
?>

    <!-- Article header with banner -->
    <header style="<?php $the_image_styles(); ?>"> <<-- This function call works

        <?php
        if ($has_overlay) :
            $banner_colour  = get_field('banner_colour');
            $banner_opacity = number_format( get_field('banner_opacity') / 100, 2 );
            // Style string for imageoverlay
            $the_overlay_styles = function() use ($banner_colour, $banner_opacity){
                echo "background:{$banner_colour}; opacity:{$banner_opacity}";
            };
        ?>

        <div style="<?php the_overlay_styles(); ?>"></div> <<-- This call never executes
        <?php endif; ?>
        <h1><?php the_title(); ?></h1>
    </header>


<?php else: ?>

Answer 1

You're defining a $the_overlay_styles variable, which references a closure. To call that, you'd do $the_overlay_styles();.

But don't. Just define it like a normal function to begin with:

function the_overlay_styles() {

You know what though, don't even do that. Just create a variable here! Far less messy.

$the_overlay_styles = "background: $banner_colour; opacity: $banner_opacity";

Now you can just echo $the_overlay_styles when you need it.