Add TypeScript implementations for Lecture 05

Lecture 05/Typescript/LSP/LSPFollowed.ts

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+// 1. DepositOnlyAccount interface: only allows deposits
+interface DepositOnlyAccount {
+    deposit(amount: number): void
+}
+
+// 2. WithdrawableAccount interface: allows deposits and withdrawals
+interface WithdrawableAccount extends DepositOnlyAccount {
+    withdraw(amount: number): void
+}
+
+class SavingAccount implements WithdrawableAccount {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Savings Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        if (this.balance >= amount) {
+            this.balance -= amount
+            console.log(`Withdrawn: ${amount} from Savings Account. New Balance: ${this.balance}`)
+        } else {
+            console.log("Insufficient funds in Savings Account!")
+        }
+    }
+}
+
+class CurrentAccount implements WithdrawableAccount {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Current Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        if (this.balance >= amount) {
+            this.balance -= amount
+            console.log(`Withdrawn: ${amount} from Current Account. New Balance: ${this.balance}`)
+        } else {
+            console.log("Insufficient funds in Current Account!")
+        }
+    }
+}
+
+class FixedTermAccount implements DepositOnlyAccount {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Fixed Term Account. New Balance: ${this.balance}`)
+    }
+}
+
+class BankClient {
+    private withdrawableAccounts: WithdrawableAccount[]
+    private depositOnlyAccounts: DepositOnlyAccount[]
+
+    constructor(
+        withdrawableAccounts: WithdrawableAccount[],
+        depositOnlyAccounts: DepositOnlyAccount[]
+    ) {
+        this.withdrawableAccounts = withdrawableAccounts
+        this.depositOnlyAccounts = depositOnlyAccounts
+    }
+
+    processTransactions(): void {
+        for (const acc of this.withdrawableAccounts) {
+            acc.deposit(1000)
+            acc.withdraw(500)
+        }
+
+        for (const acc of this.depositOnlyAccounts) {
+            acc.deposit(5000)
+        }
+    }
+}
+
+function main(): void {
+    const withdrawableAccounts: WithdrawableAccount[] = [
+        new SavingAccount(),
+        new CurrentAccount()
+    ]
+
+    const depositOnlyAccounts: DepositOnlyAccount[] = [
+        new FixedTermAccount()
+    ]
+
+    const client = new BankClient(withdrawableAccounts, depositOnlyAccounts)
+    client.processTransactions()
+}
+
+main()
+
+/**
+ * If a .ts file has no imports or exports, TypeScript treats it as a global script.
+ * Adding `export {}` marks the file as a module and prevents
+ * "Duplicate identifier 'SavingAccount'" errors.
+ */
+export {}

Lecture 05/Typescript/LSP/LSPFollowedWrongly.ts

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+// Account interface
+interface Account {
+    deposit(amount: number): void
+    withdraw(amount: number): void
+}
+
+class SavingAccount implements Account {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Savings Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        if (this.balance >= amount) {
+            this.balance -= amount
+            console.log(`Withdrawn: ${amount} from Savings Account. New Balance: ${this.balance}`)
+        } else {
+            console.log("Insufficient funds in Savings Account!")
+        }
+    }
+}
+
+class CurrentAccount implements Account {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Current Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        if (this.balance >= amount) {
+            this.balance -= amount
+            console.log(`Withdrawn: ${amount} from Current Account. New Balance: ${this.balance}`)
+        } else {
+            console.log("Insufficient funds in Current Account!")
+        }
+    }
+}
+
+class FixedTermAccount implements Account {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Fixed Term Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        throw new Error("Withdrawal not allowed in Fixed Term Account!")
+    }
+}
+
+class BankClient {
+    private accounts: Account[]
+
+    constructor(accounts: Account[]) {
+        this.accounts = accounts
+    }
+
+    processTransactions(): void {
+        for (const acc of this.accounts) {
+            acc.deposit(1000)
+
+            // Explicit type checking instead of true substitutability
+            if (acc instanceof FixedTermAccount) {
+                console.log("Skipping withdrawal for Fixed Term Account.")
+            } else {
+                try {
+                    acc.withdraw(500)
+                } catch (e: any) {
+                    console.log(`Exception: ${e.message}`)
+                }
+            }
+        }
+    }
+}
+
+function main(): void {
+    const accounts: Account[] = []
+    accounts.push(new SavingAccount())
+    accounts.push(new CurrentAccount())
+    accounts.push(new FixedTermAccount())
+
+    const client = new BankClient(accounts)
+    client.processTransactions()
+}
+
+main()
+
+/**
+ * If a .ts file has no imports or exports, TypeScript treats it as a global script.
+ * Adding `export {}` marks the file as a module and prevents
+ * "Duplicate identifier 'SavingAccount'" errors.
+ */
+export {}

Lecture 05/Typescript/LSP/LSPViolated.ts

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+// Account interface
+interface Account {
+    deposit(amount: number): void
+    withdraw(amount: number): void
+}
+
+class SavingAccount implements Account {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Savings Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        if (this.balance >= amount) {
+            this.balance -= amount
+            console.log(`Withdrawn: ${amount} from Savings Account. New Balance: ${this.balance}`)
+        } else {
+            console.log("Insufficient funds in Savings Account!")
+        }
+    }
+}
+
+class CurrentAccount implements Account {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Current Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        if (this.balance >= amount) {
+            this.balance -= amount
+            console.log(`Withdrawn: ${amount} from Current Account. New Balance: ${this.balance}`)
+        } else {
+            console.log("Insufficient funds in Current Account!")
+        }
+    }
+}
+
+class FixedTermAccount implements Account {
+    private balance: number = 0
+
+    deposit(amount: number): void {
+        this.balance += amount
+        console.log(`Deposited: ${amount} in Fixed Term Account. New Balance: ${this.balance}`)
+    }
+
+    withdraw(amount: number): void {
+        throw new Error("Withdrawal not allowed in Fixed Term Account!")
+    }
+}
+
+class BankClient {
+    private accounts: Account[]
+
+    constructor(accounts: Account[]) {
+        this.accounts = accounts
+    }
+
+    processTransactions(): void {
+        for (const acc of this.accounts) {
+            acc.deposit(1000)
+
+            // LSP violation: assuming all accounts support withdrawal
+            try {
+                acc.withdraw(500)
+            } catch (e: any) {
+                console.log(`Exception: ${e.message}`)
+            }
+        }
+    }
+}
+
+// Equivalent of Java main
+function main(): void {
+    const accounts: Account[] = []
+    accounts.push(new SavingAccount())
+    accounts.push(new CurrentAccount())
+    accounts.push(new FixedTermAccount())
+
+    const client = new BankClient(accounts)
+    client.processTransactions()
+}
+
+main()
+
+/**
+ * If a .ts file has no imports or exports, TypeScript treats it as a global script.
+ * Adding `export {}` marks the file as a module and prevents
+ * "Duplicate identifier 'SavingAccount'" errors.
+ */
+export {}