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
{
...
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