Whitelisted Functions

use Centum\Twig\WhitelistedFunctionsExtension;
use Twig\Environment;

/** @var Environment $twig */

$twig->addExtension(
    new WhitelistedFunctionsExtension(
        [
            "ucfirst",
            "lcfirst",
            "number_format",
            // ...
        ]
    )
);

Within your Twig files, you can now use these functions:

{{ ucfirst('the first letter will be capitalised.') }}

For bonus points, set your whitelisted functions in a config file. ;)