Rosetta Example: Delegates

package req nx

nx::Class create Delegator {

  # The class Delegator has a property named "delegatee" which is an
  # object:

  :property delegatee:object

  # The method "operation" decides, whether it deletates the action to
  # another object, or it performs the action itself.

  :public method operation {} {
    if {[info exists :delegatee]} {
      ${:delegatee} operation
    } else {
      return "default implementatiton"

nx::Class create Delegatee {

  # The class "Delgatee" might receice invocations from the class
  # "Delegator"

  :public method operation {} {
    return "delegatee implementatiton"

Demonstrating the behavior in a shell:

Create a Delegator, which has no delegatee defined. Therefore delegator performs the action by itself, the default implementation.

% set a [Delegator new]
% $a operation
default implementatiton

Now, we set the delegatee; therefore, the delegatee will perform the action.

% $a configure -delegatee [Delegatee new]
% $a operation
delegatee implementatiton