Generalized Functors - Realizing Command Design Pattern in C++

March 06, 2008 Generalized Functors Dr. Partha Pratim Das Interra Systems (India) Pvt. Ltd. Realizing Command Design Pattern in C++

Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

What is a Design Pattern? ,[object Object],[object Object],[object Object]

Essential Elements of a Design Pattern ,[object Object],[object Object],[object Object],[object Object]

Sample Design Patterns Command Composite Abstract Factory Iterator Proxy Singleton Visitor Behavioral Structural Creational

Command Design Pattern The World of Delegation

“ Check @ Diner” – A Command Pattern ,[object Object],[object Object],[object Object]

“ Compose & Send Mail” – A Command Pattern ,[object Object],[object Object],[object Object]

Command Pattern ,[object Object],[object Object]

Command Pattern ,[object Object]

Command Pattern ,[object Object],[object Object],[object Object],[object Object],[object Object]

Command Pattern ,[object Object],[object Object],[object Object]

Command Pattern ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Command Pattern ,[object Object],[object Object],[object Object],[object Object]

Command Pattern Macro / Composite Command

Command Pattern ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Command Pattern: Request-in-Object

Sample Command Pattern Usage ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Sample Command Pattern Usage ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Sample Command Pattern Usage ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

How to Implement Command Pattern? ,[object Object],[object Object],[object Object]

Function Pointers ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Function Pointers ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Function Pointers ,[object Object],[object Object],[object Object],[object Object]

Function Pointers ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Function Pointers – Replace Switch / IF Statements ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Function Pointers – Late Binding / Virtual Function ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Function Pointers – Callbacks ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Function Pointers ,[object Object],[object Object],[object Object],[object Object],[object Object]

Functors Function Objects in C++

Functors / Closures ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Basic Functor ,[object Object],[object Object],[object Object],[object Object],[object Object]

Functors: Elementary Example ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Functors: Examples from STL ,[object Object],[object Object],vector<int> V(100); generate(V.begin(), V.end(), rand);

Functors: Examples from STL ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Functors: Examples from STL ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Generalized Functors Basic Notions

Generalized Functors ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Generalized Functors ,[object Object],[object Object],class Functor { public: void operator()(); // other member functions private: // implementation goes here FunctorImpl *pImpl_; };

Generalized Functors ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Generalized Functors ,[object Object],[object Object],[object Object],template <typename ResultType> class Functor { ... }; template <typename ResultType, typename Parm1> class Functor { ... }; template <typename ResultType, typename Parm1, typename Parm2> class Functor { ... };

Generalized Functors ,[object Object],[object Object],[object Object],[object Object],int VarArgIntSum(int nParam, ...) { va_list va; va_start(va, nParam); for(int i = 0 , sum = 0 ; i < nParam; i++) { int& val = va_arg(va, int); sum += val; } va_end(va); return sum; }

Helper Templates ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Typelist ,[object Object],[object Object],[object Object],[object Object]

Typelist ,[object Object],[object Object],template <class T, class U> struct Typelist { typedef T Head; typedef U Tail; }; typedef Typelist<char, Typelist<signed char, unsigned char> > CharList; typedef Typelist<char, Typelist<signed char, Typelist<unsigned char, NullType> > > AllCharTypes;

Typelist: Compute Length ,[object Object],[object Object],template <class T, class U> struct Length< Typelist<T, U> > { enum { value = 1 + Length<U>::value }; }; template <class TList> struct Length; template <> struct Length<NullType> { enum { value = 0 }; };

Typelist: Index a Type ,[object Object],[object Object],[object Object],template <class Head, class Tail, unsigned int i> struct TypeAt<Typelist<Head, Tail>, i> { typedef typename TypeAt<Tail, i - 1>::Result Result; }; template <class Head, class Tail> struct TypeAt<Typelist<Head, Tail>, 0> { typedef Head Result; }; template <class Head, class Tail> struct TypeAt;

Typelist: Arbitrary Number of Types ,[object Object],#define TYPELIST_1(T1) Typelist<T1, NullType> #define TYPELIST_2(T1, T2) Typelist<T1, TYPELIST_1(T2) > #define TYPELIST_3(T1, T2, T3) Typelist<T1, TYPELIST_2(T2, T3) > #define TYPELIST_4(T1, T2, T3, T4) Typelist<T1, TYPELIST_3(T2, T3, T4) > //... //#define TYPELIST_50(...) ...

Functor Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Functor Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

The Functor ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

The Functor: Forwarding Operator ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Using Functor // Define a Functor that accepts an int and // a double and returns a double. Functor<double, TYPELIST_2(int, double)> myFunctor; // Invoke it. operator()(double, int) is generated. double result = myFunctor(4, 5.6); // Wrong invocation. double result = myFunctor(); // error! // operator()() is invalid because // FunctorImpl<double, TYPELIST_2(int, double)> // does not define one.

Using Functor ,[object Object]

References ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Generalized Functors - Realizing Command Design Pattern in C++

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