Copy a record that has some fields unset to another record.

  partial <- UserProfile("Alice", "alice@example.com")
  copy <- UserProfile()
  copy :=: partial
  stdout.println(`Copy set?: ${copy?}`)

defines module qa.operators.copypartialrecord

  defines class

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

      UserProfile()
        ->
          name as String
          email as String
        this.name :=: name
        this.email :=: email
        //phone remains unset

      default operator ?
      default operator $
      default operator :=:

  defines program

    CopyPartialRecordDemo()
      stdout <- Stdout()

      //Only name and email are set, phone is unset
      partial <- UserProfile("Alice", "alice@example.com")
      stdout.println(`Source: ${partial}`)
      stdout.println(`Source set?: ${partial?}`)

      //Copy transfers everything — including unset phone
      copy <- UserProfile()
      copy :=: partial
      stdout.println(`Copy: ${copy}`)
      stdout.println(`Copy set?: ${copy?}`)