Module: Nanoc::Helpers::Capturing

Included in:
Filtering, HTMLEscape, Rendering
Defined in:
lib/nanoc/helpers/capturing.rb

Overview

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.

Examples:

Capturing content for a summary


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

Showing captured content in a sidebar


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

Instance Method Summary collapse

Instance Method Details

#capture(&block) ⇒ String

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

Returns:

  • (String)

    The captured result



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# File 'lib/nanoc/helpers/capturing.rb', line 132

def capture(&block)
  # Get erbout so far
  erbout = eval('_erbout', block.binding)
  erbout_length = erbout.length

  # Execute block
  yield

  # 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(name, params = {}, &block) ⇒ void #content_for(item, name) ⇒ String

Overloads:

  • #content_for(name, params = {}, &block) ⇒ void

    This method returns an undefined value.

    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.

    By default, capturing content with the same name will raise an error if the newly captured content differs from the previously captured content. This behavior can be changed by providing a different :existing option to this method:

    • :error: When content already exists and is not identical, raise an error.

    • :overwrite: Overwrite the previously captured content with the newly captured content.

    • :append: Append the newly captured content to the previously captured content.

    Parameters:

    • name (Symbol, String)

      The base name of the attribute into which the content should be stored

    Options Hash (params):

    • existing (Symbol)

      Can be either :error, :overwrite, or :append

  • #content_for(item, name) ⇒ String

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

    Parameters:

    • item (Nanoc::Int::Item)

      The item for which to get the capture

    • name (Symbol, String)

      The name of the capture to fetch

    Returns:

    • (String)

      The stored captured content



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# File 'lib/nanoc/helpers/capturing.rb', line 62

def content_for(*args, &block)
  if block_given? # Set content
    # Get args
    case args.size
    when 1
      name = args[0]
      params = {}
    when 2
      name = args[0]
      params = args[1]
    else
      raise ArgumentError, 'expected 1 or 2 argument (the name ' \
        "of the capture, and optionally params) but got #{args.size} instead"
    end
    name = args[0]
    existing_behavior = params.fetch(:existing, :error)

    # Capture
    content = capture(&block)

    # Prepare for store
    snapshot_contents = @item.reps[:default].unwrap.snapshot_contents
    capture_name = "__capture_#{name}".to_sym
    case existing_behavior
    when :overwrite
      snapshot_contents[capture_name] = ''
    when :append
      snapshot_contents[capture_name] ||= ''
    when :error
      if snapshot_contents[capture_name] && snapshot_contents[capture_name] != content
        # FIXME: get proper exception
        raise "a capture named #{name.inspect} for #{@item.identifier} already exists"
      else
        snapshot_contents[capture_name] = ''
      end
    else
      raise ArgumentError, 'expected :existing_behavior param to #content_for to be one of ' \
        ":overwrite, :append, or :error, but #{existing_behavior.inspect} was given"
    end

    # Store
    snapshot_contents[capture_name] << content
  else # Get content
    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]

    rep = item.reps[:default].unwrap

    # Create dependency
    if @item.nil? || item != @item.unwrap
      dependency_tracker = @config._context.dependency_tracker
      dependency_tracker.bounce(item.unwrap)

      unless rep.compiled?
        raise Nanoc::Int::Errors::UnmetDependency.new(rep)
      end
    end

    rep.snapshot_contents["__capture_#{name}".to_sym]
  end
end