functorExample.cpp

Illustrates the use of functors

See also:

Functors in the ARIA overview

#include <string>
#include "Aria.h"


/*
  This is a class that has some callback methods. Functors which refer to these
  callbacks will be passed to the DriverClass.  
*/
class CallbackContainer
{
public:

  void callback1();
  void callback2(int i);
  bool callback3(const char *str);
};

void CallbackContainer::callback1()
{
  printf("CallbackContainer::callback1 called.\n");
}

void CallbackContainer::callback2(int i)
{
  printf("CallbackContainer::callback2 called with argument of '%d'\n", i);
}

bool CallbackContainer::callback3(const char *str)
{
  printf("CallbackContainer::callback3 called with argument of '%s'.\n", str);
  return(true);
}

/* 
 * Functors can also invoke global functions.
 */

void globalCallback()
{
  printf("globalCallback() called.\n");
}


/*
  This is a "driver" class. It takes three functors of different types and
  will invoke the three functors. This is a typical use of
  functors: to pass information or event notifications between loosely
  coupled objects.
*/
class DriverClass
{
public:

  void invokeFunctors();

  void setCallback1(ArFunctor *func) {myFunc1=func;}
  void setCallback2(ArFunctor1<int> *func) {myFunc2=func;}
  void setCallback3(ArRetFunctor1<bool, const char *> *func) {myFunc3=func;}


protected:

  ArFunctor *myFunc1;
  ArFunctor1<int> *myFunc2;
  ArRetFunctor1<bool, const char *> *myFunc3;
};

void DriverClass::invokeFunctors()
{
  bool ret;

  printf("Invoking functor1... ");
  myFunc1->invoke();

  printf("Invoking functor2... ");
  myFunc2->invoke(23);
     

  /*
     For functors with return values, use invorkeR() instead of invoke()
     to get the return value.  The invoke() function can also be used to invoke
     the functor, but the return value is lost.  (And is a possible source
     of memory leaks if you were supposed to free a pointer returned.)
  */
  printf("Invoking functor3... ");
  ret=myFunc3->invokeR("This is a string argument");
  if (ret)
    printf("\t-> functor3 returned 'true'\n");
  else
    printf("\t-> functor3 returned 'false'\n");
}

int main()
{
  CallbackContainer cb;
  DriverClass driver;

  ArFunctorC<CallbackContainer> functor1(cb, &CallbackContainer::callback1);
  ArFunctor1C<CallbackContainer, int> functor2(cb, &CallbackContainer::callback2);
  ArRetFunctor1C<bool, CallbackContainer, const char *>
    functor3(cb, &CallbackContainer::callback3);

  driver.setCallback1(&functor1);
  driver.setCallback2(&functor2);
  driver.setCallback3(&functor3);

  driver.invokeFunctors();

  /* You can make functors that target global functions too. */
  ArGlobalFunctor globalFunctor(&globalCallback);
  printf("Invoking globalFunctor... ");
  globalFunctor.invoke();

  /* You can also include the values of arguments in an ArFunctor object, if you
   * want to use the same value in every invocation of the functor.
   */
  ArFunctor1C<CallbackContainer, int> functor4(cb, &CallbackContainer::callback2, 42);
  printf("Invoking functor with constant argument... ");
  functor4.invoke();

  /* Functors can be downcast to parent interface classes, as long as their invocation
   * does not require arguments.
   */
  ArFunctor* baseFunctor = &functor4;
  printf("Invoking downcast functor... ");
  baseFunctor->invoke();


  return(0);
}

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