E07580: must return a JSON

What went wrong

A function or method is required to return JSON type but returns something else.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 887 (Why must the $$ operator always return JSON in EK9?)

How to fix it

1. Change return type to JSON

Common causes

• JSON serialization operator returning wrong type
• API response type mismatch

See also

• E07580: JSON return required (this error)
• E07570: String return required

Examples

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

Fails with E07580: must return a JSON

#!ek9
defines module error.e07580.bad

  defines class

    Label
      text <- "label"

      //'$$' converts to JSON
      default operator ?

      operator $$ as pure
        <- rtn as String: text

Fixed: Return JSON

#!ek9
defines module error.e07580.good

  defines class

    Label
      text <- "label"

      default operator ?

      operator $$ as pure
        <- rtn as JSON: JSON("text", JSON(text))

Questions and answers

These Q&A entries show E07580 and its fix:

• Q887: Why must the $$ operator always return JSON in EK9?
• Q1255: Create me a Product record and use the SINGLE-dollar $ operator to convert it to a plain-text human-readable String.
• Q1258: Create me an Invoice class with a DOUBLE-dollar $$ operator that returns a JSON value — no plain-text formatting, only JSON.