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Blockenspiel is a helper library designed to make it easy to implement DSL blocks. It is designed to be comprehensive and robust, supporting most common usage patterns, and working correctly in the presence of nested blocks and multithreading.

Blockenspiel is a helper library providing several different strategies for implementing DSL blocks. It supports both DSLs that take a block parameter and those that do not. For example:

# Call DSL block with parameter
configure_me do |config|
  config.add_foo(1)
  config.add_bar(2)
end

# Call DSL block without parameter
configure_me do
  add_foo(3)
  add_bar(4)
end

To support the above usage, you can do this:

# Implement DSL block methods
class ConfigMethods
  include Blockenspiel::DSL
  def add_foo(value)
    # do something
  end
  def add_bar(value)
    # do something
  end
end

# Implement configure_me method
def configure_me(&block)
  Blockenspiel.invoke(block, ConfigMethods.new)
end

By default, Blockenspiel uses a mixin technique (proposed by the late Why The Lucky Stiff) to support parameterless blocks without the complications introduced by instance_eval. It supports nested blocks and multithreaded access, and provides a variety of tools for handling the typical issues you may encounter when writing DSLs.

For more detailed usage and examples, see Blockenspiel.rdoc.

For an extended analysis of different ways to implement DSL blocks, see ImplementingDSLblocks.rdoc.

• Ruby 1.8.7, Ruby 1.9.1 or later, JRuby 1.5 or later, or Rubinius 1.0 or later.

gem install blockenspiel

• Implementing wildcard DSL methods using method_missing doesn’t work. I haven’t yet decided on the right semantics for this case, or whether it is even a reasonable feature at all.

• Including Blockenspiel::DSL in a module (rather than a class) is not yet supported, but this is planned for a future release.

• Installing on Windows may be a challenge because blockenspiel includes a native extension. I’m considering evaluating Luis Lavena’s rake-compiler to simplify this process.

Documentation is available at dazuma.github.com/blockenspiel/rdoc

Source code is hosted on Github at github.com/dazuma/blockenspiel

Contributions are welcome. Fork the project on Github.

Build status: <img src=“https://secure.travis-ci.org/dazuma/blockenspiel.png” />

Report bugs on Github issues at github.org/dazuma/blockenspiel/issues

Contact the author at dazuma at gmail dot com.

Blockenspiel is written by Daniel Azuma (www.daniel-azuma.com/).

The mixin implementation is based on a concept by the late Why The Lucky Stiff, documented in his 6 October 2008 blog posting entitled “Mixing Our Way Out Of Instance Eval?”. The original link has disappeared along with its author, but you may find copies or mirrors out there.

The unmixer code is based on Mixology, version by Patrick Farley, anonymous z, Dan Manges, and Clint Bishop. The MRI C extension and the JRuby code were adapted from Mixology 0.1, and have been stripped down and modified to support Ruby 1.9 and JRuby >= 1.2. The Rubinius code was adapted from unreleased code in the Mixology source tree and modified to support Rubinius 1.0. I know Mixology 0.2 is now available, but its Rubinius support is not active, and I’d rather keep the unmixer bundled with Blockenspiel for now to reduce dependencies.

The dsl_attr_writer and dsl_attr_accessor feature came from a suggestion by Luis Lavena.

Copyright 2008-2012 Daniel Azuma.

All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

• Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

• Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

• Neither the name of the copyright holder, nor the names of any other contributors to this software, may be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.