Editing Apache Groovy (section)

====Closures====
According to Groovy's documentation: "Closures in Groovy work similar to a 'method pointer', enabling code to be written and run in a later point in time".<ref>{{cite web |url=http://groovy.codehaus.org/Closures |title=Groovy - Closures |url-status=dead |archive-url=https://web.archive.org/web/20120522213410/http://groovy.codehaus.org/Closures |archive-date=2012-05-22 }}</ref> Groovy's closures support free variables, i.e. variables that have not been explicitly passed as a parameter to it, but exist in its declaration context, [[partial application]] (that it terms '[[currying]]'<ref name=":0" />), delegation, implicit, typed and untyped parameters.

When working on Collections of a determined type, the closure passed to an operation on the collection can be inferred:

<syntaxhighlight lang="groovy">
list = [1, 2, 3, 4, 5, 6, 7, 8, 9]

/* 
 * Non-zero numbers are coerced to true, so when it % 2 == 0 (even), it is false.
 * The type of the implicit "it" parameter can be inferred as an Integer by the IDE.
 * It could also be written as:
 * list.findAll { Integer i -> i % 2 }
 * list.findAll { i -> i % 2 }
 */
def odds = list.findAll { it % 2 }

assert odds == [1, 3, 5, 7, 9]
</syntaxhighlight>

A group of expressions can be written in a closure block without reference to an implementation and the responding object can be assigned at a later point using delegation:

<syntaxhighlight lang="groovy">
// This block of code contains expressions without reference to an implementation
def operations = {
  declare 5
  sum 4
  divide 3
  print
}
</syntaxhighlight>
<syntaxhighlight lang="groovy">
/* 
 * This class will handle the operations that can be used in the closure above. Another class
 * could be declared having the same methods, but using, for example, webservice operations
 * in the calculations.
 */
class Expression {
  BigDecimal value

  /* 
   * Though an Integer is passed as a parameter, it is coerced into a BigDecimal, as was 
   * defined. If the class had a 'declare(Integer value)' method, it would be used instead.
   */
  def declare(BigDecimal value) {
    this.value = value
  }
  
  def sum(BigDecimal valueToAdd) {
    this.value += valueToAdd
  }
  
  def divide(BigDecimal divisor) {
    this.value /= divisor
  }
  
  def propertyMissing(String property) {
    if (property == "print") println value
  }
}
</syntaxhighlight>
<syntaxhighlight lang="groovy">
// Here is defined who is going to respond the expressions in the block of code above.
operations.delegate = new Expression()
operations()
</syntaxhighlight>