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Power Groovy DSL Features

In this chapter, we will cover some more advanced Groovy features. Coincidentally,
these are also the features that, along with closures, allow us to extend and
manipulate the language in order to create DSLs. We will cover a lot of ground
in this chapter, including the following important features:

• Named parameters: To begin, we will look at this simple but effective
  feature, and see how maps passed as parameters act as named parameters
  to a method.


• Command chains: We will cover how, when chaining methods together, we
  can omit the dot notation to give us a simple command chain DSL pattern.


• Builders: We will cover how to use Groovy builders to rapidly construct
  anything from web pages and XML to Swing UIs. While looking at Groovy
  builders, we will also introduce the native Groovy support for tree-based
  DOM structures, by looking at the built-in GPath operators in the
  Groovy language.


• SwingBuilder: We will add a quick and simple UI to our Twitter DSL,
  by using the SwingBuilder class.


• Method pointers: We will cover method pointers as a useful way to
  create aliases.


• Meta Object Protocol: We will cover the inner workings of Groovy's Meta
  Object Protocol (MOP).


• How builders work: Once we have covered the concepts behind the MOP,
  we will revisit Groovy builders to understand how they are implemented
  using features from the MOP.


• ExpandoMetaClass: Finally, we will take a look at ExpandoMetaClass,
  which is one of the most interesting Groovy classes as it provides the keys to
  dynamically change the behavior of any existing class, including Java classes,
  on the fly.