E07210: 'default' of operators can only support '?' operator with function delegate fields

What went wrong

You're using 'default operator' on a class with function delegate fields. Function delegates only support the '?' operator for auto-generation.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 834 (Why can't I use 'default operator <=>' on a record with a...)

Note

Function delegates can only meaningfully be checked for set/unset. Comparing function references for equality is not supported.

How to fix it

1. Use only 'default operator ?' with function fields
2. Implement other operators manually

See also

• E07210: function delegate field limits operators (this error)
• E07200: property type missing operator

Examples

Every example is compiled by the EK9 compiler: the first fails exactly as captioned, the others fix it.

Fails with E07210: 'default' of operators can only support '?' operator with function delegate fields

#!ek9
defines module error.e07210.bad

  defines record

    Rule
      check as Check?

      Rule()
        -> callback as Check
        this.check: callback

      default operator <=>

      default operator ?

      //A function cannot be compared, so '<=>' cannot be generated over it

  defines function

    Check() as abstract
      -> text as String
      <- rtn as Boolean?

Fixed: Default only '?', and write the operators over the data

#!ek9
defines module error.e07210.good

  defines record

    Rule
      name as String?
      check as Check?

      default private Rule()

      //Only '?' may be defaulted over a function delegate

      Rule()
        ->
          ruleName as String
          callback as Check

        this.name: ruleName
        this.check: callback
      operator <=> as pure
        -> other as Rule
        <- rtn as Integer: name <=> other.name

      default operator ?

      //Write the sameness over the data, not the function

      operator #? as pure
        <- rtn as Integer: #?name

  defines function

    Check() as abstract
      -> text as String
      <- rtn as Boolean?

Questions and answers

These Q&A entries show E07210 and its fix:

• Q834: Why can't I use 'default operator <=>' on a record with a function delegate field?