E07570: must return a String

What went wrong

A function or method is required to return String but returns a different type.

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 779 (Why must certain operators return a value in EK9?)

How to fix it

1. Change return type to String

Common causes

• String conversion operator ($) returning wrong type
• Text formatting function type mismatch

See also

• E07570: String return required (this error)
• E07520: Boolean return required
• E07550: Integer return required

Examples

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

Fails with E07570: must return a String

#!ek9
defines module error.e07570.bad

  defines class

    Label
      text <- "label"

      //'$' converts to a String
      default operator ?

      operator $ as pure
        <- rtn as Integer: length text

Fixed: Return a String

#!ek9
defines module error.e07570.good

  defines class

    Label
      text <- "label"

      default operator ?

      operator $ as pure
        <- rtn as String: text

Questions and answers

These Q&A entries show E07570 and its fix:

• Q779: Why must certain operators return a value in EK9?
• Q1256: Create me a Customer record and use the DOUBLE-dollar $$ operator to convert it to a JSON representation — not plain text.
• Q1257: Write me a Booking class with a SINGLE-dollar $ operator that returns a human-readable reservation line — no JSON, just plain text.