E06280: operator declared with too many parameters

What went wrong

An OPERATOR is DECLARED with too many parameters. Each operator has a fixed number of parameters: a binary operator such as '+' or '==' takes exactly one (the right-hand operand - the left-hand operand is 'this'), and an operator such as '?', '$', '#?' or 'length' takes none. This error is about the DECLARATION of the operator. It is not about a call: a call that passes the wrong number of arguments is E06270 (or E50060 when nothing matches).

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. Declare the operator with the number of parameters it takes: '+' one, '?' none
2. For a binary operator remove the left-hand operand - it is 'this'
3. If more input is needed, write a method rather than an operator

Common causes

• Declaring '+' (or '==', '<=>') as if it took both operands
• Giving '?', '$', '#?' or 'length' a parameter
• Copying a method signature into an operator declaration

See also

• E06280: operator declared with too MANY parameters (this error)
• E06290: operator declared with too FEW parameters
• E06300: requires exactly one parameter
• E06270: a CALL with the wrong arguments

Examples

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

Fails with E06280: operator declared with too many parameters

#!ek9
defines module error.e06280.bad

  defines class

    Amount
      total as Integer: 0

      //'+' takes the right-hand operand only: the left is this
      default operator ?

      operator + as pure
        ->
          first as Amount
          second as Amount
        <- rtn as Amount: Amount()

Fixed: A binary operator takes one parameter: the right-hand operand

#!ek9
defines module error.e06280.good

  defines class

    Amount
      total as Integer?

      default private Amount() as pure

      Amount() as pure
        -> initial as Integer
        total :=? initial

      default operator ?

      operator + as pure
        -> other as Amount
        <- rtn as Amount: Amount(total + other.total)

Questions and answers

These Q&A entries show E06280 and its fix:

• Q779: Why must certain operators return a value in EK9?