Multiblock

Ruby methods can accept only one block at a time. Multiblock helps to build multiple-block wrappers that can be passed to Ruby methods in pleasant way.

Add this line to your application's Gemfile:

gem 'multiblock'

And then execute:

$ bundle

Or install it yourself as:

$ gem install multiblock

Obtain multiblock wrapper instance

wrapper = Multiblock::Wrapper.new

# or via shortcut
wrapper = Multiblock.wrapper

Register blocks simply by calling methods on a multiblock wrapper instance and passing actual Ruby callable objects (procs, lamdas, etc.) along:

wrapper = Multiblock.wrapper
wrapper.foo { "foo" }
wrapper.bar { |arg| "bar with #{arg}"}

Then call registered blocks:

wrapper.call(:foo)
# => "foo"

wrapper.call(:bar, "argument")
# => "bar with argument"

When calling a block under unregistered name nil is returned by default:

wrapper.call(:bar)
# => nil

But you can supply a block that will be called by default in place of unregistered one:

wrapper = Multiblock.wrapper { "default" }
wrapper.call(:bar)
# => "default"

Multiblock shines in situations when you would like to pass multiple blocks to a method. Perhaps to handle its different outcomes.

Since Ruby methods accepts only one block at a time, we simulate passing multiple blocks with this nice-looking syntax:

process(message) do |on|
  on.success { puts "ok" }
  on.failure { puts "fail" }
end

To make it work, let's define process method in following way:

def process(message)
  wrapper = Multiblock.wrapper

  # wrap blocks
  yield(wrapper)

  # do actual processing...

  if result == "success"
    wrapper.call(:success)
  else
    wrapper.call(:failure)
  end
end

Another example which kinda resembles respond_with feature from Ruby on Rails ActionController:

def respond_with(object)
  wrapper = Multiblock.wrapper
  yield(wrapper)

  # assume that request.format returns either 'json' or 'xml'
  wrapper.call(request.format, object)
end

respond_with(object) do |format|
  format.xml  { |object| render :xml  => object.to_xml  }
  format.json { |object| render :json => object.to_json }
end

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request