Variables Implícitas en una Clausura

Within a Groovy Closure, several variables are defined that have special meaning:

• it

  If you have a Closure that takes a single argument, you may omit the parameter definition of the Closure, like so:

  def clos = { print it }
  clos( "hi there" )              //prints "hi there"
  

• this, owner, and delegate
  • this : as in Java, this refers to the instance of the enclosing class where a Closure is defined
  • owner : the enclosing object (this or a surrounding Closure)
  • delegate : by default the same as owner, but changeable for example in a builder or ExpandoMetaClass

  Example:

  ~/Lgroovy/closures$ cat -n ThisDelegate.groovy 
       1  def clos = new Class1().closure
       2  clos.delegate = this
       3  clos()
       4  
       5  class Class1 {
       6    def closure = {
       7      println "Inside closure"
       8      println "this = "+this
       9      println "this.class.name = "+this.class.name
      10      println "delegate = "+delegate
      11      println "delegate.class.name = "+delegate.class.name
      12      println "owner = "+owner
      13      println "owner.class.name = "+owner.class.name
      14  
      15      def nestedClos = {
      16        println " Inside nestedClos"
      17        println " this = "+this
      18        println " delegate = "+delegate
      19        println " owner.class.name = "+owner.class.name
      20      }
      21  
      22      nestedClos()
      23    }
      24  }
  ~/Lgroovy/closures$ groovy ThisDelegate.groovy 
  Inside closure
  this = Class1@57d840cd
  this.class.name = Class1
  delegate = ThisDelegate@5d04e28b
  delegate.class.name = ThisDelegate
  owner = Class1@57d840cd
  owner.class.name = Class1
      Inside nestedClos
      this = Class1@57d840cd
      delegate = Class1$_closure1@78ff9053
      owner.class.name = Class1$_closure1