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 collapses the whole object. Write 'override operator ?' if a partially-filled object should count as set.

See Q1087 for basic isSet. 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")
      stdout.println(`Contact: ${partial}`)

      //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?}

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: isSet, ?, individual, check, partial, unset, field