E07510: operator must not be declared pure

What went wrong

You've marked an operator 'pure' but it shouldn't be - this operator is expected to modify state (mutating operator).

Worked examples

Compilable examples demonstrating this error and the correct fix:

• ek9 -q 241 (What are mutation operators and how do they differ from p...)

Operators that must not be pure

• '++' and '--' (increment and decrement)
• ':=:', ':~:' and ':^:' (copy, merge and replace)
• '+=', '-=', '*=' and '/=' (compound assignment)

Rationale

These operators modify state by design.

How to fix it

1. Remove 'pure' modifier

See also

• E07510: mutating operator has 'pure' (this error)
• E07500: pure operator missing 'pure'

Examples

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

Fails with E07510: operator must not be declared pure

#!ek9
defines module error.e07510.bad

  defines class

    Wallet
      amount <- 0.0

      holding() as pure
        <- rtn as Float: amount

      //Copy changes this object, so it cannot be pure
      default operator ?

      operator :=: as pure
        -> other as Wallet
        amount :=: other.holding()

Fixed: Remove 'as pure' from a mutating operator

#!ek9
defines module error.e07510.good

  defines class

    Wallet
      amount <- 0.0

      holding() as pure
        <- rtn as Float: amount

      default operator ?

      operator :=:
        -> other as Wallet
        amount :=: other.holding()

Questions and answers

These Q&A entries show E07510 and its fix:

• Q241: What are mutation operators and how do they differ from pure operators?