The compiler reports E08030 on my discount lookup. What is wrong and how do I fix it?

← Debugging and Troubleshooting · Ref: Q993

E08030 means you called an accessor on an Optional, Result or Iterator (get(), ok(), error(), next()) without first proving it holds a value. It is only raised for those types: an ordinary value such as a Float that might be unset can be used directly, and the result is simply unset too.

IN THIS CODE:

lookupDiscount returns an Optional of Float - empty for an unknown product. The failing code calls .get() straight away:

  lookupDiscount()
    -> productCode as String
    <- rtn as Optional of Float: Optional() of Float
    if productCode == "PREMIUM"
      rtn: Optional(0.20)

  basePrice <- 100.0
  discount <- lookupDiscount("PREMIUM")
  finalPrice <- basePrice - (basePrice * discount.get())   // ERROR E08030: not checked before access
  stdout.println($finalPrice)

THE FIX:

Use a declaration guard, which declares the variable AND checks that it is set:

  if discount <- lookupDiscount(productCode)
    finalPrice <- basePrice - (basePrice * discount.get())

The body only runs when the Optional holds a discount, so the get() inside it is safe. 'if discount?' after a separate declaration works the same way.

ALTERNATIVELY:

Ask the Optional for a default, so there is nothing to check:

  rate <- lookupDiscount(productCode).getOrDefault(0.0)
  finalPrice <- basePrice - (basePrice * rate)

This uses 0.0 (no discount) when the Optional is empty.

Example

defines module qa.debugging.diagnoseerror

  defines function

    lookupDiscount() as pure
      -> productCode as String
      <- rtn as Optional of Float: Optional() of Float

      premiumCode <- "PREMIUM"
      standardCode <- "STANDARD"

      if productCode == premiumCode
        rtn: Optional(0.20)
      else if productCode == standardCode
        rtn: Optional(0.10)

  defines program

    DiagnoseErrorDemo()
      stdout <- Stdout()

      basePrice <- 100.0

      //Correct: the guard checks the Optional, so get() inside the body is safe
      if discount <- lookupDiscount("PREMIUM")
        finalPrice <- basePrice - (basePrice * discount.get())
        stdout.println(`Discounted price: ${finalPrice}`)

      //Correct: getOrDefault needs no check - an unknown product gets 0.0
      standardDiscount <- lookupDiscount("UNKNOWN").getOrDefault(0.0)
      regularPrice <- basePrice - (basePrice * standardDiscount)
      stdout.println(`Regular price: ${regularPrice}`)

Common mistakes

E08030 — Calling get() on an Optional that has not been checked is rejected. Use a guard 'if v <- expr()' (or 'if v?') before get(), or getOrDefault(). See ek9 -h E08030.

Incorrect:

      discount <- lookupDiscount("PREMIUM")
      finalPrice <- basePrice - (basePrice * discount.get())
      stdout.println(`Discounted price: ${finalPrice}`)

Correct:

      if discount <- lookupDiscount("PREMIUM")
        finalPrice <- basePrice - (basePrice * discount.get())
        stdout.println(`Discounted price: ${finalPrice}`)

E01073 — 'null' does not exist in EK9. Use a guard 'if v <- expr()' to check the Optional, or the ? suffix: 'if discount?'. See ek9 -h E01073.

Incorrect:

      discount <- lookupDiscount("PREMIUM")
      if discount != null
        finalPrice <- basePrice - (basePrice * discount.get())
        stdout.println(`Discounted price: ${finalPrice}`)

Correct:

      if discount <- lookupDiscount("PREMIUM")
        finalPrice <- basePrice - (basePrice * discount.get())
        stdout.println(`Discounted price: ${finalPrice}`)

Other ways to ask this

Diagnose this E08030 error in my EK9 code
Why is the compiler saying unsafe access on this line?
Help me understand and fix E08030 in this code

Coming from another language?

E08030 in EK9 is like calling Optional.get() in Java without isPresent(), or unwrap() in Rust - except EK9 rejects it at compile time instead of throwing at runtime. There is no escape hatch.

Keywords: Optional, E08030, access, fix, guard, unsafe, getOrDefault, diagnose