Add a constant() test for testing values against constants.

[markstory]

Quite a few applications use constants to make various magic numbers
and strings more memorable, and usable. Would it be useful to have a
test in twig allowing you to check values against global and class
constants. Proposed implementation would be:

{% if my_value is constant('ADMIN_LVL') %}
or
{% if post.state is constant('Post::PUBLISHED') %}

[arnaud-lb]

Why not a constant filter instead ? This would allow to retrieve the value of the constant.

e.g. {{ 'ADMIN_LVL'|constant }}
and {% if my_value == 'ADMIN_LVL'|constant %}

[arnaud-lb]

an other use case for retrieving the value of a constant is to use constants as filter arguments, as in {{ myDate|date('DATE_W3C'|constant) }}

[markstory]

I guess it could be done as a filter as well. I originally thought of a test because I normally use constants in if statements. I usually think of filters as output manipulation, and I don't normally output constants. But the date() case is interesting.

[timotheemoulin]

I made my own extension to do that : https://github.com/tehem/TwigConstantExtension