memento.c

design_patterns code设计模式书中的源码 对学习设计模式的人很有帮助的

/*
*/
class Memento;
/*
*/
class State;

class Originator {
public:
    Memento* CreateMemento();
    void SetMemento(const Memento*);
    // ...
private:
    State* _state;      // internal data structures
    // ...
};
/*
*/
class Memento {
public:
    // narrow public interface
    virtual ~Memento();
private:
    // private members accessible only to Originator
    friend class Originator;
    Memento();
/*
*/
    void SetState(State*);
    State* GetState();
    // ...
private:
    State* _state;
    // ...
};
/*
*/
#include "Geom.H"
class ConstraintSolverMemento;
class ConstraintSolver;

class Graphic {
  public:
   void  Move(const Point&);
};

/*
*/
class Graphic;
    // base class for graphical objects in the graphical editor

class MoveCommand {
public:
    MoveCommand(Graphic* target, const Point& delta);
    void Execute();
    void Unexecute();
private:
    ConstraintSolverMemento* _state;
    Point _delta;
    Graphic* _target;
};
/*
*/
class ConstraintSolver {
public:
    static ConstraintSolver* Instance();
/*
*/
    void Solve();
    void AddConstraint(
        Graphic* startConnection, Graphic* endConnection
    );
    void RemoveConstraint(
        Graphic* startConnection, Graphic* endConnection
    );
/*
*/
    ConstraintSolverMemento* CreateMemento();
    void SetMemento(ConstraintSolverMemento*);
private:
    // nontrivial state and operations for enforcing
    // connectivity semantics
};
/*
*/
class ConstraintSolverMemento {
public:
    virtual ~ConstraintSolverMemento();
private:
    friend class ConstraintSolver;
    ConstraintSolverMemento();

    // private constraint solver state
};
/*
*/
void MoveCommand::Execute () {
    ConstraintSolver* solver = ConstraintSolver::Instance();
    _state = solver->CreateMemento(); // create a memento
    _target->Move(_delta);
    solver->Solve();
}
/*
*/
void MoveCommand::Unexecute () {
    ConstraintSolver* solver = ConstraintSolver::Instance();
    _target->Move(-_delta);
    solver->SetMemento(_state); // restore solver state
    solver->Solve();
}
/*
*/
class IterationState;
/*
*/
template <class Item>
class Collection {
public:
    Collection();

    IterationState* CreateInitialState();
    void Next(IterationState*);
    bool IsDone(const IterationState*) const;
    Item CurrentItem(const IterationState*) const;
    IterationState* Copy(const IterationState*) const;

    void Append(const Item&);
    void Remove(const Item&);
    // ...
};
/*
*/
class ItemType {
public:
    void Process();
    // ...
};
/*
*/
class IterationState {
};
void dummy () {
/*
*/
Collection<ItemType*> aCollection;
IterationState* state;

state = aCollection.CreateInitialState();

while (!aCollection.IsDone(state)) {
    aCollection.CurrentItem(state)->Process();
    aCollection.Next(state);
}
delete state;
/*
*/
}
/*
*/