Check which fields are set in a partially-initialised record.

  partial <- ContactInfo("Alice")
  if partial?
    stdout.println("set")

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 ANY-field semantics: 1 of 3 is set, so true
      stdout.println(`Is set?: ${partial?}`)

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

${partial <> null}

${partial?}