Add a 'getMatrixChildren()' method to RepeaterMatrixPage objects

object-hook-methods-RepeaterMatrixPage_get_matrix_children.php

<?php

declare(strict_types=1);

namespace ProcessWire;

/**
 * Custom method that gets nested child RepeaterMatrixPage objects as a PageArray for the
 * RepeaterMatrixPage executed upon. This simulates accessing RepeaterMatrix items as pages
 *
 * Usage, can be used on any RepeaterMatrix page with nested children:
 * $page->repeater_matrix_field->first()->getMatrixChildren(); // => PageArray
 */
$wire->addHookMethod('RepeaterMatrixPage::getMatrixChildren', function(HookEvent $e) {
    $targetMatrixPage = $e->object;
    $repeaterMatrixField = $targetMatrixPage->getForField()->name;

    $targetMatrixPageMatched = false;
    $targetMatrixPageChildren = [];

    // Get field on page where the target matrix page exists
    $targetMatrixField = $targetMatrixPage->getForPage()->$repeaterMatrixField;

    foreach ($targetMatrixField as $repeaterMatrixPage) {
        if ($repeaterMatrixPage->id === $targetMatrixPage->id) {
            $targetMatrixPageMatched = true;

            continue;
        }

        if (!$targetMatrixPageMatched) {
            continue;
        }

        if ($repeaterMatrixPage->getDepth() === $targetMatrixPage->getDepth() + 1) {
            $targetMatrixPageChildren[] = $repeaterMatrixPage;

            continue;
        }

        // When the depth is at or below the target page depth, we've retrieved all of the children
        if ($repeaterMatrixPage->getDepth() <= $targetMatrixPage->getDepth()) {
            break;
        }
    }

    $e->return = PageArray($targetMatrixPageChildren);
});