Bank example

Bank.swift

enum Transaction {
    case deposit, withdraw
}

class Bank {
    
    typealias Account = (String, Double)
    typealias AccountTransaction = (Double, Account) -> Account
    
    static func deposit(amount : Double, account : (name : String, balance : Double)) -> Account {
        let newBalance : Double = account.balance + amount
        return (account.name, newBalance)
    }
    
    static func withdraw(amount : Double, account : (name : String, balance : Double)) -> Account {
        let newBalance : Double = account.balance - amount
        return (account.name, newBalance)
    }
    
    static func chooseTransaction(transaction: Transaction) -> AccountTransaction {
        switch transaction {
        case .deposit:
            return Bank.deposit
        case .withdraw:
            return Bank.withdraw
        }
    }
}

class Vault {
    static func accessVault(password: String) -> String {
        
        func openVault() -> String {
            return "Vault opened"
        }
        
        func closeVault() -> String {
            return "Vault closed"
        }
        
        if password == "secret" {
            return openVault()
        } else {
            return closeVault()
        }
    }
}

Playground.swift

var account1 = ("State Bank Personal", 1011.10)
var account2 = ("State Bank Business", 24309.63)

Bank.chooseTransaction(transaction: .deposit)(63.17, account1)

Vault.accessVault(password: "secret")