Phalcon volt - addFunction vs addFilter

phalcon volt addFilter addFunction.php

<?php

$compiler = new \Phalcon\Mvc\View\Engine\Volt\Compiler();

$compiler->addFunction("test1", function($resolvedArgs, $exprArgs) {

        $value = $exprArgs[0]['expr']['value'];
        return str_replace('$', '&euro;', $value);
    });

$compiler->addFilter("test2", function($resolvedArgs, $exprArgs) {

        return "str_replace('$', '&euro;', $resolvedArgs)";
    });

$compiler->addFunction("test3", function($resolvedArgs, $exprArgs) {

        $value = $exprArgs[0]['expr']['value'];
        return "str_replace('$', '&euro;', '$value')";
    });

echo highlight_string($compiler->compileString('{{ test1("100 $") }}'),1);
echo '<br />';
echo highlight_string($compiler->compileString('{{ "100 $"|test2 }}'),1);
echo '<br />';
echo highlight_string($compiler->compileString('{{ test3("100 $") }}'),1);

/**
test1: <?php echo 100 &euro;; ?>
test2: <?php echo str_replace('$', '&euro;', '100 $'); ?>
test3: <?php echo str_replace('$', '&euro;', '100 $'); ?>
 */