How do I use the #? hashcode operator on a record?

← Operators and Expressions · Ref: Q1047

Records can use 'default operator' to auto-generate #? from all fields. The generated hashcode combines the hash values of every field.

  defines record
    Coordinate
      latitude as Float: 0.0
      longitude as Float: 0.0
      default operator

Usage:

  point <- Coordinate(51.5, -0.12)
  hash <- #? point

The default operator generates #? that combines #?latitude and #?longitude. You can also define it manually if you need custom logic:

  operator #? as pure
    <- rtn as Integer: #?latitude + #?longitude

The #? operator always returns Integer. It must be pure. Records with default operator also get ==, $, :=:, and other operators automatically.

See Q911 for what #? means. See Q1053 for manual #? on a class. See Q1055 for default vs manual operators. See Q116 for what default operator generates.

Example

defines module qa.operators.hashcoderecord

  defines record

    Coordinate
      latitude as Float: 0.0
      longitude as Float: 0.0

      Coordinate()
        ->
          latitude as Float
          longitude as Float
        this.latitude :=: latitude
        this.longitude :=: longitude

      default operator

  defines program

    HashcodeRecordDemo()
      stdout <- Stdout()

      pointA <- Coordinate(51.5, -0.12)
      pointB <- Coordinate(51.5, -0.12)
      pointC <- Coordinate(48.8, 2.35)

      hashA <- #? pointA
      hashB <- #? pointB
      hashC <- #? pointC

      stdout.println(`A hash: ${hashA}`)
      stdout.println(`B hash: ${hashB}`)
      stdout.println(`C hash: ${hashC}`)
      stdout.println(`A == B: ${pointA == pointB}`)
      stdout.println(`A == C: ${pointA == pointC}`)

Other ways to ask this

How does #? work on records in EK9?
Show me hashcode with a record type
Can records have a hashcode operator?

Coming from another language?

Java: records auto-generate hashCode(). Python: dataclasses can auto-generate __hash__(). EK9: 'default operator' on records generates #? from all fields.

Keywords: record, default, operator, integer, hashcode