Groovy scope - how to access script variable in a method

Question

I have a question about scoping rules in Groovy. In the following snippet, I have three variables, a has local scope, b has script scope, and c should get script scope as well using the @Field annotation.

#!/usr/bin/groovy import groovy.transform.Field;  //println org.codehaus.groovy.runtime.InvokerHelper.getVersion()  def a = 42; b = "Tea" @Field def c = "Cheese"  void func() {     // println a // MissingPropertyException     println b // prints "Tea"     println c // prints "Cheese" with groovy 2.1.2, MissingPropertyException with groovy 1.8.6  }  class Main {     def method()     {         // println a // MissingPropertyException         // println b // MissingPropertyException         // println c // MissingPropertyException with both 1.8.6. and 2.1.2     }  }  func(); new Main().method(); 

I get MissingPropertyExceptions on the lines indicated with comments. The exceptions on a are expected, as that variable has local scope. But I would expect b to be accessible inside method() - it isn't. @Field doesn't do anything in groovy 1.8.6, although after upgrading it works, so I guess that is an old bug. Nevertheless, c is inaccessible inside method() with either version.

So my questions are:

1. Why can't I access a variable annotated with @Field inside method()?
2. How can I refer to a script variable inside method()?

Answer 1

When you have methods or statements outside of a class declaration in a groovy script, an implicit class is created. To answer your questions:

1. In your example, func() can access the field c because they are both members of the implicit class. The Main class is not, so it can't.

2. You need to pass a reference to the script variable to method(). One way is to pass the implicitly defined binding object, through which you can access all the script scope variables.

Example:

#!/usr/bin/groovy import groovy.transform.Field;  //println org.codehaus.groovy.runtime.InvokerHelper.getVersion()  def a = 42; b = "Tea" @Field def c = "Cheese"  void func() {     // println a // MissingPropertyException     println b // prints "Tea"     println c // prints "Cheese" with groovy 2.1.2, MissingPropertyException with groovy 1.8.6  }  class Main {     def scriptObject     def binding      def method()     {         // println a // MissingPropertyException         println binding.b         println scriptObject.c     } }  func(); new Main(scriptObject: this, binding: binding).method();