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CfgScript delegate Expressions

| Literals | Assigment | Operator | Instanceof | Delegates | Lambda |

Delegates are a powerfull mechanism to implement function level dispatching, callbacks and signal/slot mechanism.



DelegateExpression
: 'delegate' TypeOrVarName '.' MethodName
| 'delegate' '(' Expression ')' '.' MethodName
| MethodName
;

The delegate converts a class or object method in a Delegate instance.
Delegate is a shortcut to  acdk::lang::dmi::DmiDelegate.

There are three forms of delegate usage:

1.
'delegate' TypeOrVarName '.' MethodName

TypeOrVarName can be
  • a variable
  • a member variable (like acdk.lang.System.out)
  • a Class name

MethodName is the name of a method.

2.
'delegate' '(' Expression ')' '.' MethodName

The Expression has to be evaluated to an Object instance.

3.
'delegate' MethodName

This form of delegate is only valid if used inside a - static or non static - method.

See Sample:



class AClass 
{
  String prefix;
  AClass(String pref)
  {
      prefix = pref;
  }
  // callback function
  static RString GetGerText(String name) 
  { 
    return "Hallo " + name; 
  }
  // other callback function
  static RString GetEngText(String name) 
  { 
    return "Hello " + name; 
  }
  // non static method callback function
  String getEngText(String name)
  {
    return "Hello " + prefix + " " + name;
  }
  // this method uses a delegate:
  static void useDelegate(Delegate del) 
  {
    out.println(del.call("ACDK"));
  }
  static void DelegateInsideClass()
  {
    // inside a class method with 'delegate' methods can be used directly
    useDelegate(delegate GetEngText);
  }
  void delegateInsideClass()
  {
    // inside a class method with 'delegate' methods can be used directly
    useDelegate(delegate getEngText);
  }
}

AClass.useDelegate(delegate (new AClass("superb")).getEngText);

// use a static method (english)
AClass.useDelegate(delegate AClass.GetGerText);
// now use english text
AClass.useDelegate(delegate AClass.GetEngText);

AClass cls = new AClass("finest");

// Delegates works also with non-static methods
AClass.useDelegate(delegate cls.getEngText);

// using expression
AClass.useDelegate(delegate (new AClass("superb")).getEngText);

// see AClass.DelegateInsideClass
AClass.DelegateInsideClass();

// see AClass.delegateInsideClass
cls.delegateInsideClass();


// what the implementation of the delegate does:
AClass.useDelegate(new DmiDelegate(AClass.GetClass(), "GetGerText"));


Delegates works also with native ACDK C++ implemented methods:

class AClass 
{
  // callback function
  static void println(String name) 
  { 
    out.println("AClass: " + name); 
  }
}
DelegateArray delegates = new DelegateArray(0);
// script implementation
delegates.append(delegate AClass.println);
// native ACDK C++ implemenation of println
delegates.append(delegate acdk.lang.System.out.println);

foreach (Delegate dlg in delegates)
{
  dlg.call("A Text");
}

See also:  Lambda.
See also:  Calling Interface.

Samples

 
Last modified 2005-05-08 18:22 by SYSTEM By Artefaktur, Ing. Bureau Kommer