Polymorphism

→ fundamental to Object-Oriented Programming

Polymorphism: Run-time / late binding / dynamic binding (normally before before compiling)

→ Runtime polymorphism: being able to assign different meanings to the same function at run-time

→ Allows to programm more abstractly

→ Polymorphism is achieved via

• inheritance

• base class pointers or references

• virtual functions

Static Binding

void display_account(const Account &acc) {
	acc.display();
	// will always use Account::display
}

Account a;
display_account(a);

Savings b;
display_account(b);
 
Checking c;
display_account(c);

Trust d;
display_account(d);

Dynamic binding (Runtime Polymorphism)

Account a;
a.withdraw(1000); // Account::withdraw()

Savings b;
b.withdraw(1000); // Savings::withdraw()

Checking c;
c.withdraw(1000); // Checking::withdraw()

Trust d;
d.withdraw(1000); // Trust::withdraw()

Account *p = new Trust();
P->withdraw(1000); // Trust::withdraw()

// withdraw method is virtual in Account

void display_account(const Account &acc)
{
	acc.display();
	// will always call the display method
	// depending on the object's type
	// at RUN-TIME
}

Account a;
display_account(a);

Savings b;
display_account(b);

Checking c;
display_account(c);

Trust d;
display_account(d);

// example

using Base class pointer

Account *p1 = new Account();
Account *p2 = new Savings();
Account *p3 = new Checking();
Account *p4 = new Trust();

p1->withdraw(1000); // Account::withdraw
p2->withdraw(1000); // Savings::withdraw
p3->withdraw(1000); // Checking::withdraw
p4->withdraw(1000); // Trust::withdraw

// delete the pointers

// usecase

Account *p1 = new Account();
Account *p2 = new Savings();
Account *p3 = new Checking();
Account *p4 = new Trust();

// for array
Account *array [] = {p1, p2, p3, p4};

for (auto i=0; i<4; ++i)
	array[i]->withdraw(1000);

// for vector
std::vector<Account *> accounts{p1,p2,p3,p4};
for (auto acc_ptr:accounts)
	acc_ptr->withdraw(1000);