E07220: 'default' is not supported on this operator

What went wrong

You're using 'default' with an operator that doesn't support auto-generation. Only specific operators can be auto-generated.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 116 (What does 'default operator' generate?)

[SUPPORTED 'DEFAULT' OPERATORS] 'default' can generate only these operators, each from the type's fields:

• '?' - the set-check (true only when ALL fields are set)
• '<=>' (ordered) or '==' (equatable only) - the type's sameness; '<>', '<', '<=', '>' and '>=' are then generated from it, never asked for (that is E07181)
• '$' (String form), '$$' (JSON form), '#?' (hash code), ':=:' (shallow copy)
• 'close' - closes the type's closeable properties

The bare 'default operator' asks for all of these that the type can have.

[UNSUPPORTED - MUST IMPLEMENT MANUALLY] Every other operator - arithmetic ('+', '-', '*', '/', '++', '--'), 'empty', 'contains', 'length' and the rest - has a meaning only the type can decide.

Semantics

• 'default operator ?' = true only if ALL fields are set (own and inherited)
• 'default operator #?/$/$$' = UNSET if object completely empty

How to fix it

1. Use only supported operators with 'default'
2. Implement unsupported operators manually

The [EXAMPLE] section below shows 'default operator empty' on a record, and the record writing its own 'empty'.

Common causes

• Using 'default' with unsupported operator symbol
• Trying to auto-generate arithmetic operators

See also

• E07220: unsupported default operator (this error)
• E07230: default operator with parameters/body

Examples

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

Fails with E07220: 'default' is not supported on this operator

#!ek9
defines module error.e07220.bad

  defines record
    Basket
      items <- List() of String

      //What 'empty' means is the type's own decision
      default operator ?

      default operator empty

Fixed: Write the operator

#!ek9
defines module error.e07220.good

  defines record
    Basket
      items <- List() of String

      default operator ?

      operator empty as pure
        <- rtn as Boolean: items.empty()

Questions and answers

These Q&A entries show E07220 and its fix:

• Q116: What does 'default operator' generate?