Can't suppress output in nested block helper in rails 3

This one is sort of twisting my noodle.

I have something resembling this (in a rails 3 engine if that matters)

class Builder
  def initialize
    @foos = []
  end

  def foo(&block)
    @foos << helper.capture(&block) #helper being a class that is including ActionView::Helpers
  end

  def to_html
    @foos.join "\n"
  end
end

module ApplicationHelper
  def widget
    b = Builder.new
    yield b

    b.to_html
  end
end

#in a view somewhere
<%= widget do |b| %>
  <% b.foo do %>
    static content
  <% end %>
<% end %>

Everything is working out great, but that nested static content is getting output twice -- once where I want it, and once where widget was called.

From what I have read, capture is supposed to deal with this exact problem. I am pretty sure the problem stems from how I am calling capture (from a dummy proxy class that includes ActionView::Helpers), but the problem is that b.foo call is calling a method on a class instance, not from the context of something that will be mixed into the template.

Is there any way to get around this problem? Or am I approaching this from the wrong direction. I am trying to model something fairly involved and am really happy with the api, just can't seem to get passed开发者_如何转开发 this problem.

If you modify the helper method to pass in self, which would be the current view instance, and then use this to capture, you might not have this issue. Substitute your use of helper for the provided view instance.