DefaultValueExpressionNode.php

<?php
namespace Famelo\Cider\Fluid;

/*
 * This file belongs to the package "TYPO3 Fluid".
 * See LICENSE.txt that was shipped with this package.
 */

use NamelessCoder\Fluid\Core\Parser;
use NamelessCoder\Fluid\Core\Parser\SyntaxTree\Expression\AbstractExpressionNode;
use NamelessCoder\Fluid\Core\Rendering\RenderingContextInterface;
use NamelessCoder\Fluid\Core\Variables\VariableExtractor;

/**
 * Default value shorthand expression will cycle through each variable until one
 * is found that is not empty
 */
class DefaultValueExpressionNode extends AbstractExpressionNode {

	/**
	 * Pattern which detects a default value expression in shorthand syntax
	 * syntax, e.g. {checkvar||'foobar'}.
	 */
	public static $detectionExpression = '/
		(
			{                                # Start of shorthand syntax
				(?:                          # Math expression is composed of...
					[a-zA-Z0-9.\\\'\"]+            # Check variable side
					[\s]*\|\|[\s]*		     # check for a || to be the first thing after the variable
					[a-zA-Z0-9.|\s\\\'\"]+         # at least one more variable behind the or, maybe more
				)
			}                                # End of shorthand syntax
		)/x';

	/**
	 * @param RenderingContextInterface $renderingContext
	 * @param string $expression
	 * @param array $matches
	 * @return mixed
	 */
	public static function evaluateExpression(RenderingContextInterface $renderingContext, $expression, array $matches) {
		$variables = explode('||', $expression);
		$variables = array_map(array(__CLASS__, 'trimPart'), $variables);
		foreach ($variables as $variable) {
			if (substr($variable, 0, 1) == '\'') {
				return trim($variable, '\'');
			} else if (substr($variable, 0, 1) == '"') {
				return trim($variable, '"');
			} else {
				$value = self::getTemplateVariable($variable, $renderingContext);
				$checkResult = Parser\SyntaxTree\BooleanNode::convertToBoolean($value);
				if ($checkResult === TRUE) {
					return $value;
				}
			}
		}
	}

	/**
	 * @param mixed $candidate
	 * @param RenderingContextInterface $renderingContext
	 * @return mixed
	 */
	protected static function getTemplateVariable($candidate, RenderingContextInterface $renderingContext) {
		$variables = $renderingContext->getVariableProvider()->getAll();
		$extractor = new VariableExtractor();
		return $extractor->getByPath($variables, $candidate);
	}
}

Template.html

<p>
  output first variable thats not false/null {foo||bar||foobar}
</p>

<p>
  output variable or default value {foo||'foobar'}
</p>