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Nanoc::Helpers::Capturing

Provides functionality for “capturing” content in one place and reusing this content elsewhere.

For example, suppose you want the sidebar of your site to contain a short summary of the item. You could put the summary in the meta file, but that’s not possible when the summary contains eRuby. You could also put the sidebar inside the actual item, but that’s not very pretty. Instead, you write the summary on the item itself, but capture it, and print it in the sidebar layout.

This helper has been tested with ERB and Haml. Other filters may not work correctly.

@example Capturing content for a summary

<% content_for :summary do %>
  <p>On this item, nanoc is introduced, blah blah.</p>
<% end %>

@example Showing captured content in a sidebar

<div id="sidebar">
  <h3>Summary</h3>
  <%= content_for(@item, :summary) || '(no summary)' %>
</div>

@example Showing captured content in a sidebar the old, deprecated way (do not use or I will become very angry)

<div id="sidebar">
  <h3>Summary</h3>
  <%= @item[:content_for_summary] || '(no summary)' %>
</div>

Public Instance Methods

capture(&block) click to toggle source

Evaluates the given block and returns its contents. The contents of the block is not outputted.

@return [String] The captured result

# File lib/nanoc/helpers/capturing.rb, line 150
def capture(&block)
  # Get erbout so far
  erbout = eval('_erbout', block.binding)
  erbout_length = erbout.length

  # Execute block
  block.call

  # Get new piece of erbout
  erbout_addition = erbout[erbout_length..-1]

  # Remove addition
  erbout[erbout_length..-1] = ''

  # Depending on how the filter outputs, the result might be a
  # single string or an array of strings (slim outputs the latter).
  erbout_addition = erbout_addition.join if erbout_addition.is_a? Array

  # Done.
  erbout_addition
end
content_for(*args, &block) click to toggle source

@overload content_for(name, &block)

Captures the content inside the block and stores it so that it can be
referenced later on. The same method, {#content_for}, is used for
getting the captured content as well as setting it. When capturing,
the content of the block itself will not be outputted.

For backwards compatibility, it is also possible to fetch the captured
content by getting the contents of the attribute named `content_for_`
followed by the given name. This way of accessing captures is
deprecated.

@param [Symbol, String] name The base name of the attribute into which
  the content should be stored

@return [void]

@overload content_for(item, name)

Fetches the capture with the given name from the given item and
returns it.

@param [Nanoc::Item] item The item for which to get the capture

@param [Symbol, String] name The name of the capture to fetch

@return [String] The stored captured content
# File lib/nanoc/helpers/capturing.rb, line 99
def content_for(*args, &block)
  if block_given? # Set content
    # Get args
    if args.size != 1
      raise ArgumentError, "expected 1 argument (the name " + 
        "of the capture) but got #{args.size} instead"
    end
    name = args[0]

    # Capture and store
    content = capture(&block)
    @site.captures_store[@item, name.to_sym] = content
  else # Get content
    # Get args
    if args.size != 2
      raise ArgumentError, "expected 2 arguments (the item " +
        "and the name of the capture) but got #{args.size} instead"
    end
    item = args[0]
    name = args[1]

    # Create dependency
    current_item = @site.compiler.dependency_tracker.top
    if item != current_item
      Nanoc::NotificationCenter.post(:visit_started, item)
      Nanoc::NotificationCenter.post(:visit_ended,   item)

      # This is an extremely ugly hack to get the compiler to recompile the
      # item from which we use content. For this, we need to manually edit
      # the content attribute to reset it. :(
      # FIXME clean this up
      if !@site.captures_store_compiled_items.include? item
        @site.captures_store_compiled_items << item 
        item.forced_outdated = true
        item.reps.each do |r|
          raw_content = item.raw_content
          r.content = { :raw => raw_content, :last => raw_content }
          @site.compiler.send(:compile_rep, r)
        end
      end
    end

    # Get content
    @site.captures_store[item, name.to_sym]
  end
end

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