Question

I want to define a closure which takes one argument (which i refer to with it )
sometimes i want to pass another additional argument to the closure.
how can i do this?

Answer 1

You could set the second argument to a default value (such as null):

def cl = { a, b=null ->
  if( b != null ) {
    print "Passed $b then "
  }
  println "Called with $a"
}

cl( 'Tim' )          // prints 'Called with Tim'
cl( 'Tim', 'Yates' ) // prints 'Passed Yates then Called with Tim

Another option would be to make b a vararg List like so:

def cl = { a, ...b ->
  if( b ) {
    print "Passed $b then "
  }
  println "Called with $a"
}

cl( 'Tim' )                    // prints 'Called with Tim'
cl( 'Tim', 'Yates' )           // prints 'Passed [Yates] then Called with Tim
cl( 'Tim', 'Yates', 'Groovy' ) // prints 'Passed [Yates, Groovy] then Called with Tim