What does default ? report for a partially-initialised record?

← Operators and Expressions · Ref: Q1088

A partially-initialised object is UNSET under default ?:

  partial <- ContactInfo("Alice")
  if not partial?
    stdout.println("not fully set")

With 1 of 3 fields set, default ? returns false - it uses ALL-field (flattened-aggregate) semantics, so a single unset field - own or inherited - collapses the whole object. An unset object has no $ text either, so interpolating it (`${partial}`) prints nothing at all - test with ? first. Write 'override operator ?' if a partially-filled object should count as set.

See Q1089 for custom override operator ?.

Example

defines module qa.operators.checkpartialset

  defines class

    ContactInfo
      name <- String()
      email <- String()
      phone <- String()

      ContactInfo()
        -> name as String
        this.name :=: name
        //email and phone remain unset

      default operator

  defines program

    CheckPartialSetDemo()
      stdout <- Stdout()

      //Only name is set — email and phone remain unset
      partial <- ContactInfo("Alice")
      //Interpolating the whole object prints nothing: $ of an unset object is unset

      //default ? uses ALL-field semantics: only 1 of 3 is set, so this is FALSE
      stdout.println(`Is set?: ${partial?}`)

      //Compare with fully unset object
      blank <- ContactInfo()
      stdout.println(`Empty set?: ${blank?}`)

Common mistakes

E01073 — 'null' does not exist in EK9 — check an object's overall set-status with the '?' operator (partial?) instead of comparing to null. See ek9 -h E01073 for details.

Incorrect:

${partial <> null}

Correct:

${partial?}

Other ways to ask this

I have a contact with only a name filled in — is it still set?
In Java I'd check each field for null separately. Show the EK9 ALL-field semantics
Given an object with 1 of 3 fields set, confirm the default operator ? result
Test whether a partially-initialised object counts as set in EK9
Check if all fields in a record have been set.
Test whether an object is fully initialised using ?
Determine if a record has any unset fields
In Java I'd check each field for null. How do I check if an EK9 object is set?
I need to verify that a config object has all required values before using it

Coming from another language?

Java: check each field != null individually. Python: hasattr or getattr checks. EK9: default ? requires EVERY field to be set; override ? for custom logic such as partial-tolerant checks.

Keywords: fields, initialised, partial, check, validate, record, set, field, ?, isSet, unset, operator, individual