Review this design. Should I use composition instead of a large class?

Yes, this class is doing too much. It handles both user validation and notification — two separate concerns.

Split it into:
- A UserValidator class that checks names and emails
- A Notifier class that sends messages
- The main class delegates to both via composition

Benefits of composition:
- Each class has one responsibility
- You can test validation without notification
- You can swap notification implementations
- EK9 types are closed by default, so composition is the standard extension pattern

Keep each class focused on one concern. Compose them together in a coordinator class.

Example

defines module qa.gettingstarted.compositionreview

  defines class

    UserValidator
      isValidName() as pure
        -> name as String
        <- rtn as Boolean: name.length() > 0

      isValidEmail() as pure
        -> email as String
        <- rtn as Boolean: email.contains("@")

      override operator ? as pure
        <- rtn as Boolean: true

      operator $ as pure
        <- rtn as String: "UserValidator"

    Notifier
      sendWelcome()
        -> name as String
        <- rtn as String: `Welcome ${name}`

      override operator ? as pure
        <- rtn as Boolean: true

      operator $ as pure
        <- rtn as String: "Notifier"

  defines program

    CompositionDemo()
      stdout <- Stdout()

      validator <- UserValidator()
      notifier <- Notifier()

      userName <- "Alice"
      email <- "alice@example.com"

      if validator.isValidName(userName) and validator.isValidEmail(email)
        message <- notifier.sendWelcome(userName)
        stdout.println(message)

Common mistakes

E05030 — EK9 types are closed by default and cannot be extended; 'extends UserValidator' fails with E05030 - use composition instead. See ek9 -h E05030 for details.

Incorrect:

    Notifier extends UserValidator
      sendWelcome()

Correct:

    Notifier
      sendWelcome()

Other ways to ask this

Is this class doing too many things?
Should I break this class into smaller pieces?
Assess whether this class follows single responsibility

Coming from another language?

EK9 types are closed by default. Composition is the primary way to combine behavior from multiple sources.

Keywords: responsibility, review, design, composition, split