Check if a custom Twig function exists and then call it

Question

I test if a custom Twig function exists:

{% if methodExist(\'sg_datatables_render\') %}
    {{ sg_datatables_render(datatable) }}
 {% else %}
    {{ datatable_re         


        

Answer 1

I tried to replicate this, and indeed, {{ sg_datatables_render(datatable) }} seems to always cause a Twig_Error_Syntax exception when sg_datatables_render has not been registered as a Twig function.

I then tried something like this. It's ugly, but I wanted to know if it works. The idea is that a non-existing function will be created to avoid the exception being thrown:

$twig->addFunction(new Twig_Function('methodExist', function(Twig_Environment $twig, $name) {
    $hasFunction = $twig->getFunction($name) !== false;

    if (!$hasFunction) {
        // The callback function defaults to null so I have omitted it here
        return $twig->addFunction(new Twig_Function($name));
    }

    return $hasFunction;
}, ['needs_environment' => true]));

But it didn't work. I also tried to add a simple callback function to the new function with no success.

I tried the same trick with filters, i.e.:

{% if filterExists('sg_datatables_render') %}
    {{ datatable|sg_datatables_render }}
 {% else %}
    {{ datatable|datatable_render }}
{% endif %}

It didn't work either.

---

Solution 1: {{ renderDatatable(datatable) }}

Something like this does work (yay!):

$twig->addFunction(new Twig_Function('renderDatatable', function(Twig_Environment $twig, $datatable) {
    $sgFunction = $twig->getFunction('sg_datatables_render');

    if ($sgFunction !== false) {
        return $sgFunction->getCallable()($datatable);
    }

    return $twig->getFunction('datatable_render')->getCallable()($datatable);
}, ['needs_environment' => true]));

And then in Twig:

{{ renderDatatable(datatable) }}

The renderDatatable function is specific to rendering datatables, i.e. it's not a general/multipurpose function like your methodExist is, but it works. You can of course try to create a more general implementation yourself.

---

Solution 2: {{ fn('sg_datatables_render', datatable) }}

Here's a more general approach. Create an additional Twig function to accompany methodExist:

$twig->addFunction(new Twig_Function('fn', function(Twig_Environment $twig, $name, ...$args) {
     $fn = $twig->getFunction($name);

     if ($fn === false) {
         return null;
     }

     // You could add some kind of error handling here
     return $fn->getCallable()(...$args);
 }, ['needs_environment' => true]));

Then you could modify your original code to this:

{% if methodExist('sg_datatables_render') %}
    {{ fn('sg_datatables_render', datatable) }}
 {% else %}
    {{ datatable_render((datatable)) }}
{% endif %}

Or even use the ternary operator:

{{ methodExist('sg_datatables_render') ? fn('sg_datatables_render', datatable) : datatable_render(datatable) }}

---

PS

Here's how I'd write the methodExist function:

$twig->addFunction(new Twig_Function('methodExists', function(Twig_Environment $twig, $name) {
     return $twig->getFunction($name) !== false;
 }, ['needs_environment' => true]));

1. I added s to the end of the function's name because the function checks whether a method/function exists.
2. I added ['needs_environment' => true] so I can use $twig instead of $this->container->get('twig'). (Kudos to yceruto for this tip.)
3. getFunction returns false if the function doesn't exist (see the docs), so I simplified the function body to a single-line return statement.