Include ERB delimiters inside a row in an ERB block

Question

I am working on a style that displays code as well as output. Currently, it is structured in such a way that the code should be described only once and is displayed both in its source and in interpreted versions, for example:

<% code = <<PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR <div> #{ image_tag 'image.png' } </div> PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR %> <%= raw code %> <%= content_tag :pre, code, class: "prettyprint linenums" %> 

This is great and fairly easy to maintain. The problem occurs with rail assistants, for example, image_tag in the example above. The example view correctly displays the image in a div, and the corresponding HTML displays the image in the sample code. In this case, the corresponding HTML code contains an anchor tag - the results of the image_tag method, and not the call itself.

I would prefer code examples to display helper methods rather than their results. I can do this work by specifying sample code in a file, and either rendering or reading the file. I would prefer to do this work by specifying the code in a variable as above, but I cannot get the ERB delimiter to work inside a string inside an erb block. Even the simplest case <% foo = '<%= bar %>' %> does not work at all. I tried playing with syntax (e.g. <%% %%> and <%% %%> ) using data from official documentation without much success.

The only information I could find on this was here using <%= "<" + "%=" %> link_to <%= image.css_tag.humanize %> <%= "%" + ">" %> %> , which does not work in this use case (if at all).

So, is there a way to specify a string containing the trailing ERB delimiter ( %> ) in the ERB string, or am I stuck using a slightly clunkier file reading method? Thanks!

Edit:

What I would like to get is a working version of this:

 <%# Idealized code - does not work %> <% code = <<PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR <div> <% image_tag 'image.png' %> </div> PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR %> 

So, <%= raw code %> will (continue) output:

 <div> <img src="/images/image.png" alt="Image" /> </div> 

And <%= content_tag :pre, code, class: "prettyprint linenums" %> outputs:

 <pre class="prettyprint linenums"> <div> <% image_tag 'image.png' %> </div> </pre> 

Instead of what it is currently doing when using a variable that:

 <pre class="prettyprint linenums"> <div> <img src="/images/image.png" alt="Image" /> </div> </pre> 

I want users to be able to copy the sample code and paste it into a new view, without having to translate the HTML back into the helpers that produce them. I think I basically need an alternative ERB delimiter, just as ' and " (or even %q{} ) are different for strings. It seems that although the final ERB delimiter occurs inside a string, it is actually treated as the end of the block. The simplest the case <% foo = '<%= bar %>' %> somewhat demonstrates what I want to do. In the generator you can use <% foo = '<%%= bar %>' %> (or something like that ), to say that it is not processed like ERB right there and there. All this works fine when reading from a file or even in a pure rb file (for example, an assistant), but It makes sense to insert him into submission, as it should be easily manipulated by our designers.

Answer 1

If I understand you correctly, your real problem is that heredocs behave like double quotes with respect to interpolation. So, all you need is a quoting mechanism that behaves like single quotes. Ruby has many mechanisms for quoting strings, in particular we have %q{...} :

 <% code = %q{ <div> #{ image_tag 'image.png' } </div> } %> 

You can use other delimiters if you want: %q|...| , %q(...) , etc. There is still a change in course, but at least you don't need to worry about problems with interpolation.

If you really want to use heredoc, you can specify a heredoc terminator with quotes , and the corresponding citation style will apply to the content:

 <% code = <<'PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR' <div> #{ image_tag 'image.png' } </div> PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR %> 

The single quotation marks in <<'PLACE...' indicate that uniform quotation rules (i.e. interpolation) apply to the heredoc content.

---

Of course, none of these materials will work with embedded ERB as follows:

 <% code = %q{ <div> <% ... %> </div> } %> 

because the ERB parser will see the first %> as a closing delimiter for the outer part <% code... Don't be afraid, I think I have a plan that will work without involving gross hacks or too much work.

Some preliminary :

• Rails uses Erubis to handle ERB.
• Erubis allows you to change the delimiters with the :pattern option to its constructor.
• Rails uses Tilt and Sprockets to handle the template processing pipeline, this allows you to do the right thing with pancakes.js.coffee.erb in the correct order.

Using the above, you can add your own template format, which is an ERB with a different separator, and you can use Rails in this new format to process your “special” sections before normal ERB processing can mess things up.

First you need to connect the Tilt. If you look at lib/tilt/erb.rb in your Tilt installation, you will see the Erubis stuff in Tilt::ErubisTemplate below. You must have a subclass of Tilt::ErubisTemplate and provide an override of prepare that adds, say, the option :pattern => '<!--% %-->' Tilt::ErubisTemplate :pattern => '<!--% %-->' , and discards the superclass. Then register this with Tilt and Sprockets in the Rails initializer with something like this:

 Tilt.register(Your::Template::Subclass, 'klerb') # "kl" for "kludge" :) Rails.application.assets.register_engine('.klerb', Your::Template::Subclass) 

Your application should now be able to process .klerb files using <!--% ... %--> as template separators. And you can also link your klerb to erb using names like pancakes.html.erb.klerb and the file will go through klerb before ERB; this means that such templates (in a file named whatever.html.erb.klerb ):

 <!--% code = <<PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR <div> <% image_tag 'image.png' %> </div> PLACE_THE_EXAMPLE_CODE_BETWEEN_THESE_TWO_LINES_EXACTLY_AS_YOU_WANT_IT_TO_APPEAR %--> <!--%= "code = escape_the_erb_as_needed(%q{#{code}})" %--> <% do_normal_erb_stuff %> 

will do the right thing.

To implement the escape_the_erb_as_needed function escape_the_erb_as_needed you need a helper; a little experimentation should help you figure out what you need to run away and how.

All that may seem a bit complicated, but it is really quite straightforward. I added custom template processing steps using Tilt and Sprockets, and in the end it turned out to be pretty simple; figuring out what simple things needed to be done, but I already did this job for you:

• Tilt::Template , you get this based on Tilt::ErubisTemplate .
• Register with Tilt by calling Tilt.register .
• Register using the asterisks by calling Rails.application.assets.register_engine .
• ...
• Profit