PlaceholderGeneratorInterface.php

<?php

namespace Drupal\Core\Render;


/**
 * Defines an interface for turning a render array into a placeholder.
 *
 * This encapsulates logic related to generating placeholders.
 *
 * Makes it possible to determine whether a render array can be placeholdered
 * (it can be reconstructed independently of the request context), whether a
 * render array should be placeholdered (its cacheability meets the conditions),
 * and to create a placeholder.
 *
 * @see \Drupal\Core\Render\RendererInterface
 */
interface PlaceholderGeneratorInterface {
    
    /**
     * Analyzes whether the given render array can be placeholdered.
     *
     * @param array $element
     *   A render array. Its #lazy_builder and #create_placeholder properties are
     *   analyzed.
     *
     * @return bool
     */
    public function canCreatePlaceholder(array $element);
    
    /**
     * Whether the given render array should be automatically placeholdered.
     *
     * The render array should be placeholdered if its cacheability either has a
     * cache context with too high cardinality, a cache tag with a too high
     * invalidation rate, or a max-age that is too low. Either of these would make
     * caching ineffective, and thus we choose to placeholder instead.
     *
     * @param array $element
     *   The render array whose cacheability to analyze.
     *
     * @return bool
     *   Whether the given render array's cacheability meets the placeholdering
     *   conditions.
     */
    public function shouldAutomaticallyPlaceholder(array $element);
    
    /**
     * Turns the given element into a placeholder.
     *
     * Placeholdering allows us to avoid "poor cacheability contamination": this
     * maps the current render array to one that only has #markup and #attached,
     * and #attached contains a placeholder with this element's prior cacheability
     * metadata. In other words: this placeholder is perfectly cacheable, the
     * placeholder replacement logic effectively cordons off poor cacheability.
     *
     * @param array $element
     *   The render array to create a placeholder for.
     *
     * @return array
     *   Render array with placeholder markup and the attached placeholder
     *   replacement metadata.
     */
    public function createPlaceholder(array $element);

}