What method does each EK9 operator call internally?

← Operators and Expressions · Ref: Q1003

Every EK9 operator calls a specific method on the object. Here are the key mappings:

CONVERSION OPERATORS:

  - $variable calls _string(), returns String
  - #? variable calls _hashcode(), returns Integer
  - #^ variable calls _promote(), returns a different type
  - $$ variable calls _json(), returns JSON

CHECKING OPERATORS:

  - variable? calls _isSet(), returns Boolean (suffix, no parentheses)

COMPARISON OPERATORS:

  - a == b calls _eq(), returns Boolean
  - a <> b calls _neq(), returns Boolean
  - a <=> b calls _cmp(), returns Integer (negative, zero or positive)

COPY/MERGE OPERATORS:

  - a :=: b calls _copy(), copies b into a
  - a :~: b calls _merge(), merges b into a
  - a :^: b calls _replace(), replaces a content with b

The 'default operator' keyword generates _string, _json, _hashcode, _isSet, _cmp (with _eq, _neq and the ordering comparisons derived from it) and _copy from your declared fields. It does NOT generate #^ (_promote), :~: (_merge) or :^: (_replace) - those must be written by hand, and using them on a type without them is a compile error. Implement any operator manually for custom behaviour.

Example

defines module qa.operators.methodnames

  defines record

    Sensor
      location as String: String()
      reading as Float: 0.0

      Sensor()
        ->
          location as String
          reading as Float
        this.location :=: location
        this.reading :=: reading

      default operator

  defines program

    OperatorMethodNamesDemo()
      stdout <- Stdout()

      sensor <- Sensor("Kitchen", 22.5)

      // $ calls _string()
      sensorText <- $sensor
      stdout.println(`String: ${sensorText}`)

      // #? calls _hashcode()
      sensorHash <- #? sensor
      stdout.println(`Hash: ${sensorHash}`)

      // ? calls _isSet() — suffix, no parentheses
      stdout.println(`Is set: ${sensor?}`)

      // <=> calls _cmp()
      other <- Sensor("Lounge", 20.0)
      comparison <- sensor <=> other
      stdout.println(`Compare: ${comparison}`)

Common mistakes

E50060 — EK9 objects have no toString() method — the $ prefix operator calls _string(); use $variable (or ${...} interpolation) for String conversion. See ek9 -h E50060 for details.

Incorrect:

      stdout.println(`Is set: ${sensor.toString()}`)

Correct:

      stdout.println(`Is set: ${sensor?}`)

Other ways to ask this

What is the mapping between EK9 operators and their method names?
What does each EK9 operator symbol translate to?
Show me the operator to method name mapping in EK9

Coming from another language?

EK9 operators are method calls with fixed names. $ is _string() (like Java toString), #? is _hashcode() (like Java hashCode), ? is _isSet() (like Rust is_some).

Keywords: operator, name, string, mapping, method, hashcode, promote