Functor Object Example

From FunctorObject:

Here's a stripped down version of a C++ implementation: -- PhilGoodwin

This declares an interface for functors that is used by clients. Other versions of this interface include parameter types and return values

 struct Functor
 { virtual void operator()()=0; };

This declares an adaptor that turns an object/method pair into a Functor that can be passed to a client

 template< typename Type_ >
 class FunctorFor: public Functor
 {
 public:
        typedef void(Type_::*MemberFunction)();

 private:
        Type_           *theInstance;
        MemberFunction  theMethod;

 public:
        FunctorFor(Type_ *anInstance, MemberFunction aMethod): theInstance(anInstance), theMethod(aMethod){}

        void operator()() { (theInstance->*theMethod)(); }
 };

This declares an adaptor for normal function pointers It doesn't actually do anything except add type safety

 class FunctionFunctor: public Functor
 {
 public:
        typedef void(*FunctionType)();

 private:
        Function theFunction;

 public:
        FunctionFunctor(FunctionType aFunction): theFunction(aFunction){}

        void operator() () { theFunction(); }
 };

Here are a couple of snippets that show how to add parameter and return types:

 template< typename ReturnType, typename ParameterType >
 struct FunctorR1
 { ReturnType operator() (ParameterType)=0; };

 template< typename Type_, typename ReturnType, typename ParameterType >
 class FunctorR1For: class FunctorR1<ReturnType, ParameterType>
 {
       ...
       typedef ReturnType(Type_::*MemberFunction)(ParameterType);
       ...
       ReturnType operator() (ParameterType param) { return (theInstance->*theMethod(param); }
 };

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See BlocksInJava for an example in the JavaLanguage