Question

I have a HAML template that I want to render and optionally provide a local variable to, here called post, so that it either uses the provided variable as the value of an element attribute, or falls back to an explicit default.

The code below shows what I mean, but it fails to run if post isn’t provided. Is there a clean solution to this? I have quite a few of these fields, and I’d rather not have to keep duplicating them with - if defined? statements, which is the only other alternative I can think of.

%label
  Post title
  %input{:name  => "title",
         :value => (defined? post) ? post.title : ""} }

Answer 1

Ah, turns out the real problem was that this is in Sinatra, which defines a post method to define handlers for HTTP posts, and the HAML renderer can see this.

If you provided a post variable to the renderer it hides it, so the template works fine, but otherwise post is actually a function, and so defined? is true, but clearly there’s no title property.

Just changing the name of the variable makes everything work as I expected.