Using generic views inside WordPress for a more flexible UI system. For more info see https://philkurth.com.au/articles/use-generic-views-with-data-arrays-for-a-flexible-context-independent-ui-system/

class-view.php

<?php

class View {


	public static $view_dir = '';


	/**
	 * Render View Template With Data
	 *
	 * Locates a view template and includes it within the same scope as a data object/array. This makes it possible to
	 * access raw data in the template.
	 *
	 * Note: Any data passed into this function will be casted as an array and then as an object. The final data available
	 * within a template is in the form of an object with the variable name $data.
	 *
	 * e.g.
	 *
	 *      array('name' => 'Bob', 'age' => 42)
	 *
	 * Will be converted to an object to be used as;
	 *
	 *      $data->name
	 *      $data->age
	 *
	 * @param string|null $name A named variation for the template. This is in the form {$name}.php. Can include directories, where necessary.
	 * @param object|array $data An associative array or object to use inside the template.
	 * @param string $suffix The file suffix.
	 *
	 * @return  string
	 */
	public static function prepare( $name, $data = [], $suffix = '.php' ) {

		$markup = '';
		$path = self::get_full_path( $name . $suffix );

		if ( $t = self::view_template_exists( $path ) ) {
			$data = self::prepare_data( $data );
			ob_start();
			include $path;
			$markup = ob_get_clean();
		}

		return $markup;
	}


	/**
	 * Use this to echo out templates
	 *
	 * @param $name
	 * @param array $data
	 * @param string $suffix
	 */
	public static function render( $name, $data = [], $suffix = '.php' ) {
		echo self::prepare( $name, $data, $suffix );
	}


	/**
	 * Casts data to an object for use int the template
	 *
	 * @param $data
	 *
	 * @return object
	 */
	private static function prepare_data( $data ) {

		// if data is not already an object, cast as object
		if ( ! is_object( $data ) ) {
			$data = (object) (array) $data;
		}

		return $data;
	}


	/**
	 * Making sure the template exists
	 *
	 * @param $name
	 *
	 * @return bool
	 */
	private static function view_template_exists( $name ) {
		return file_exists( $name );
	}


	/**
	 * Pieces together the full path to the file
	 *
	 * @param $name
	 *
	 * @return string
	 */
	private static function get_full_path( $name ) {
		return trailingslashit( self::$view_dir ) . ltrim( $name, '/' );
	}


}

functions.php

<?php

include 'inc/View.php';

View::$view_dir = get_stylesheet_directory() . '/templates';

index.php

<?php

get_header();

if ( have_posts() ) {
	while ( have_posts() ) {
		the_post();

		View::render( 'post-single', [
			'post_title' => get_the_title(),
			'content' => get_the_content(),
			'author' => get_the_author(),
		] );

	}
} else {
	?>
    <p>No post found.</p>
	<?php
}

get_footer();

post-single.php

<?php
$data = isset( $data ) ? $data : new stdClass();
$post_title = isset( $data->post_title ) ? $data->post_title : "";
$author = isset( $data->author ) ? $data->author : "";
$content = isset( $data->content ) ? $data->content : "";
?>
<div class="PostSingle">

	<?php if ( $post_title ): ?>
        	<h1 class="PostSingle__title"><?= $post_title ?></h1>
	<?php endif; ?>

	<?php if ( $author ): ?>
        	<div class="PostSingle__author"><?= $author ?></div>
	<?php endif; ?>

	<?php if ( $content ): ?>
        	<div class="PostSingle__content"><?= $content ?></div>
	<?php endif; ?>

</div>

template-render-example.php

<?php

View::render( 'post-single', [
  'post_title' => get_the_title(),
  'content' => get_the_content(),
  'author' => get_the_author(),
] );