No clean way to conditionally add HTML tag attributes

[aspotashev]

I want to add an attribute class="active" to an element when some condition (in C++) is true. I currently do it like this:
%a(href="/myurl" method="POST" class=(active ? "active" : ""))

Unfortunately, in this way the "class" attribute is always present, even when it's empty. This makes the resulting HTML code not very clean.

[thammi]

I am aware of the problem but was not able to find a feasible solution, yet. Do you have an idea how to solve this (preferably in a way which can be easily ported to all supported languages)?

[aspotashev]

The best I could invent for this is checking if the given expression is an empty string (e.g. using std::stringstream in C++), but removing all empty attributes is not good because some of them have effect on HTML even if they are empty, e.g. the attribute "checked" of an <input type="checkbox" ...>