Using a combination of lambda expressions and extension methods, the language can be extended by means of libraries, i.e. without changing the language itself. A small standard library makes heavy use of this.
Xtend comes with ready-to-use active annotations for common code patterns. They reside in the org.eclipse.xtend.lib.annotations plug-in/jar which must be on the class path of the project containing the Xtend files.
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