Prototype in C++
Why read if you can watch?
Watch Prototype's video tutorialBefore and after
BEFORE - The architect has done an admirable job of decoupling the client from Stooge concrete derived classes, and, exercising polymorphism. But there remains coupling where instances are actually created.
class Stooge
{
public:
virtual void slap_stick() = 0;
};
class Larry: public Stooge
{
public:
void slap_stick()
{
cout << "Larry: poke eyes\n";
}
};
class Moe: public Stooge
{
public:
void slap_stick()
{
cout << "Moe: slap head\n";
}
};
class Curly: public Stooge
{
public:
void slap_stick()
{
cout << "Curly: suffer abuse\n";
}
};
int main(void)
{
vector roles;
int choice;
while (true)
{
cout << "Larry(1) Moe(2) Curly(3) Go(0): ";
cin >> choice;
if (choice == 0)
break;
else if (choice == 1)
roles.push_back(new Larry);
else if (choice == 2)
roles.push_back(new Moe);
else
roles.push_back(new Curly);
}
for (int i = 0; i < roles.size(); i++)
roles[i]->slap_stick();
for (int i = 0; i < roles.size(); i++)
delete roles[i];
}
Larry(1) Moe(2) Curly(3) Go(0): 2
Larry(1) Moe(2) Curly(3) Go(0): 1
Larry(1) Moe(2) Curly(3) Go(0): 3
Larry(1) Moe(2) Curly(3) Go(0): 0
Moe: slap head
Larry: poke eyes
Curly: suffer abuse
AFTER - A clone() method has been added to the Stooge
hierarchy. Each derived class implements that
method by returning an instance of itself. A
Factory class has been introduced that main-
tains a suite of "breeder" objects (aka proto-
types), and knows how to delegate to the
correct prototype.
class Stooge {
public:
virtual Stooge* clone() = 0;
virtual void slap_stick() = 0;
};
class Factory {
public:
static Stooge* make_stooge( int choice );
private:
static Stooge* s_prototypes[4];
};
int main( void ) {
vector roles;
int choice;
while (true) {
cout << "Larry(1) Moe(2) Curly(3) Go(0): ";
cin >> choice;
if (choice == 0)
break;
roles.push_back(
Factory::make_stooge( choice ) );
}
for (int i=0; i < roles.size(); ++i)
roles[i]->slap_stick();
for (int i=0; i < roles.size(); ++i)
delete roles[i];
}
class Larry : public Stooge {
public:
Stooge* clone() { return new Larry; }
void slap_stick() {
cout << "Larry: poke eyes\n"; }
};
class Moe : public Stooge {
public:
Stooge* clone() { return new Moe; }
void slap_stick() {
cout << "Moe: slap head\n"; }
};
class Curly : public Stooge {
public:
Stooge* clone() { return new Curly; }
void slap_stick() {
cout << "Curly: suffer abuse\n"; }
};
Stooge* Factory::s_prototypes[] = {
0, new Larry, new Moe, new Curly
};
Stooge* Factory::make_stooge( int choice ) {
return s_prototypes[choice]->clone();
}
