Add more examples

Author: tshemsedinov

Classification/5-abstract.ts

@@ -0,0 +1,25 @@
+// Subtype polymorphism: abstract class
+
+abstract class Account {
+  constructor(protected readonly balance: number) {}
+
+  abstract describe(): string;
+}
+
+class SavingsAccount extends Account {
+  describe(): string {
+    return `Savings -> Balance: ${this.balance}`;
+  }
+}
+
+class CreditAccount extends Account {
+  describe(): string {
+    return `Credit -> Balance: ${this.balance}`;
+  }
+}
+
+const accounts: Account[] = [new SavingsAccount(5000), new CreditAccount(-750)];
+
+for (const account of accounts) {
+  console.log(account.describe());
+}

Classification/6-protocol.js

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+'use strict';
+
+// Subtype polymorphism: protocol/duck typing
+
+const describe = (entity) => {
+  if (typeof entity.describe !== 'function') {
+    throw new TypeError('Requires describe method');
+  }
+  entity.describe();
+};
+
+class SavingsAccount {
+  constructor(balance) {
+    this.balance = balance;
+  }
+
+  describe() {
+    console.log(`Savings -> Balance: ${this.balance}`);
+  }
+}
+
+class CreditAccount {
+  constructor(balance) {
+    this.balance = balance;
+  }
+
+  describe() {
+    console.log(`Credit -> Balance: ${this.balance}`);
+  }
+}
+
+describe(new SavingsAccount(5000));
+describe(new CreditAccount(-750));

Classification/7-dynamic.js

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+'use strict';
+
+// Subtype polymorphism: dynamic dispatch
+
+class Account {
+  constructor(balance) {
+    this.balance = balance;
+  }
+
+  describe() {
+    return `Balance: ${this.balance}`;
+  }
+}
+
+class SavingsAccount extends Account {
+  describe() {
+    return `Savings -> ${super.describe()}`;
+  }
+}
+
+class CreditAccount extends Account {
+  describe() {
+    return `Credit -> ${super.describe()}`;
+  }
+}
+
+const accounts = [new SavingsAccount(5000), new CreditAccount(-750)];
+
+for (const account of accounts) {
+  console.log(account.describe());
+}

Classification/8-virtual.cpp

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+// Subtype polymorphism: virtual functions and methods
+
+#include <iostream>
+#include <string>
+#include <vector>
+
+class Account {
+public:
+  explicit Account(int balance) : balance(balance) {}
+  virtual ~Account() = default;
+
+  virtual std::string describe() const {
+    return "Balance: " + std::to_string(balance);
+  }
+
+protected:
+  int balance;
+};
+
+class SavingsAccount : public Account {
+public:
+  using Account::Account;
+
+  std::string describe() const override {
+    return "Savings -> " + Account::describe();
+  }
+};
+
+class CreditAccount : public Account {
+public:
+  using Account::Account;
+
+  std::string describe() const override {
+    return "Credit -> " + Account::describe();
+  }
+};
+
+int main() {
+  std::vector<Account*> accounts;
+  accounts.push_back(new SavingsAccount(5000));
+  accounts.push_back(new CreditAccount(-750));
+
+  for (const auto& account : accounts) {
+    std::cout << account->describe() << '\n';
+  }
+}