Review this EK9 class. Does it follow EK9 best practices?

← Code Quality · Ref: Q992

This class follows several EK9 best practices:

GOOD:

- Fields are private (class default) with accessor methods
- Constructor uses -> for parameters and assigns with :
- 'default operator' generates standard operators from fields
- The describe() method returns a value rather than printing (pure)
- Named accessor methods match field names (accountHolder, currentBalance)

IMPROVEMENT OPPORTUNITIES:

- The deposit and withdraw methods could validate inputs (e.g., negative amounts)
- The class could use 'as pure' on accessor methods to declare they have no side effects
- Consider using :=? guarded assignment in withdraw to prevent negative balance
- If this class is not meant to be extended, the default closed status is correct

OVERALL: Good basic design. The separation of data (private fields) from behaviour (methods) is correct EK9 style.

Example

defines module qa.codequality.reviewclass

  defines class

    BankAccount
      accountHolder as String: String()
      currentBalance as Float: 0.0

      BankAccount()
        ->
          accountHolder as String
          currentBalance as Float
        this.accountHolder: accountHolder
        this.currentBalance: currentBalance

      accountHolder() as pure
        <- rtn as String: accountHolder

      currentBalance() as pure
        <- rtn as Float: currentBalance

      deposit()
        -> depositAmount as Float
        currentBalance := currentBalance + depositAmount

      withdraw()
        -> withdrawalAmount as Float
        currentBalance := currentBalance - withdrawalAmount

      describe() as pure
        <- rtn as String: `${accountHolder}: ${currentBalance}`

      default operator

  defines program

    ReviewClassDemo()
      stdout <- Stdout()

      account <- BankAccount("Alice Smith", 1000.0)
      stdout.println(account.describe())

      account.deposit(500.0)
      stdout.println(account.describe())

      account.withdraw(200.0)
      stdout.println(account.describe())

Common mistakes

E06180 — Class fields are private in EK9. Access them through methods: account.describe() or account.accountHolder(). Direct field access like account.accountHolder only works on records.

Incorrect:

      stdout.println(account.accountHolder)

Correct:

      stdout.println(account.describe())

Coming from another language?

EK9 classes follow encapsulation by default — fields are private, methods provide access. Use 'default operator' to auto-generate standard operators.

Keywords: quality, best practice, class, review, assess, design