Garbage Burrito

I've been having fun with blocks and HTML lately, but I realized I kind of glazed over a very important, yet enigmatic piece of the puzzle.  How do you capture the block of HTML, and append/prepend stuff to it?  To figure this out I had to dig a little.

I knew that the new and improved form_tag helper had to have this magic in it, and sure enough....

if block_given?
  content = capture(&block)
  concat(tag(:form, html_options, true) + method_tag, block.binding)
  concat(content, block.binding)
  concat("</form>", block.binding)
else
  tag(:form, html_options, true) + method_tag
end

First it checks to see if a block was provided.  If so we use the capture helper to grab the HTML from the enclosed block.  Capturing it means it ain't going to print to the screen itself.  Using the concat helper, we can "bind" new HTML to the output buffer.  This is a little confusing, because the arguments are kind of backwards, IMO.  Think of block.binding as the HTML page, and the first argument as the shtuff you want to append to it.

If there's no block, it just creates the first half of the form tag.  

Here's a simple example.  We needed to wrap all the forms in Doodlekit with a div, for HTML compliance or some other crazy CSS Wizardy.  So I overwrote the form_tag helper like this...

alias old_form_tag form_tag

def form_tag(url_for_options = {}, options = {}, *parameters_for_url, &proc)
  if block_given?
    content = capture(&proc)
    concat('<div class="form_tag">', proc.binding)
    concat(old_form_tag(url_for_options, options, parameters_for_url), proc.binding)
    concat(content, proc.binding)
    concat('</form></div>', proc.binding)
  else
    old_form_tag(url_for_options, options, parameters_for_url)
  end
end

I alias the original form_tag method, so I can still use it.  If a block is given I capture the HTML.  Print the div, print the form, print the captured content, print the end form, print the end div.

It's a little less than straight forward at first, but once you've got it your good to rock some funky erb beats.