Why can't I access class fields from outside the class in EK9?

← Classes and OOP · Ref: Q882

ALL class fields are private. Always. There is no 'public' or 'protected' modifier for fields in EK9's grammar — it does not exist.

To expose state, write a method:

  describe()
    <- rtn as String: `${userName} <${email}>`

Record fields are the opposite — ALL public. That is the key difference:
- CLASS: fields private, has methods — for objects with behaviour
- RECORD: fields public, no methods — for pure data

You cannot write 'public name as String' on a class. You cannot write a method on a record. The compiler enforces this separation.

To copy field values, use ':=:' in a constructor:

  MyClass()
    -> initialName as String
    name :=: initialName

See Q97 for class vs record. See Q95 for field visibility. See Q876 for record basics.

Example

defines module qa.classes.fields.private

  defines record

    Address
      street <- String()
      city <- String()

      Address()
        ->
          s as String
          c as String
        street :=: s
        city :=: c

      operator <=> as pure
        -> arg0 as Address
        <- rtn as Integer: street <=> arg0.street

      default operator

  defines class

    Person
      personName <- String()
      homeAddress <- Address("", "")

      Person()
        ->
          pName as String
          addr as Address
        personName :=: pName
        homeAddress :=: addr

      //Method exposes state — fields are private
      location()
        <- rtn as String: `${personName} lives in ${homeAddress.city}`

      default operator ?

  defines program

    FieldVisibility()
      stdout <- Stdout()

      //Record fields are public
      addr <- Address("123 Main", "Springfield")
      stdout.println(addr.city)

      //Class fields accessed via methods
      person <- Person("Steve", addr)
      if person?
        stdout.println(person.location())

Other ways to ask this

Are all EK9 class fields private?
How do I expose class state in EK9?
What is the visibility of fields in EK9 classes vs records?

Coming from another language?

Java: public/private/protected on fields. Python: convention-only _prefix. Kotlin: var/val with getters. EK9: class fields ALWAYS private, record fields ALWAYS public — no modifier needed or allowed.

Keywords: visibility, private, access, record, class, public, field, method