When should I use try/finally without catch in EK9?

← Control Flow · Ref: Q934

The finally block runs regardless of whether an exception occurs. Use try/finally without catch when you want cleanup but not error handling at that level.

TRY/FINALLY PATTERN

  try
    doWork()
  finally
    cleanup()       // Always runs

The exception propagates up to the caller. The finally block still executes before propagation.

TRY/CATCH/FINALLY

  try
    doWork()
  catch
    -> ex as Exception
    logError(ex)
  finally
    cleanup()       // Runs after catch too

Finally runs in all scenarios: normal completion, exception caught, or exception propagating.

WHEN TO OMIT CATCH

Omit catch when the current scope cannot meaningfully handle the error. Let exceptions propagate to a higher-level handler while still guaranteeing local cleanup.

See Q902 for try/catch syntax. See Q932 for single catch type. See Q935 for nested try/catch.

Example

defines module qa.controlflow.tryfinally

  defines function

    riskyCalculation() as pure
      ->
        x as Integer
        y as Integer
      <-
        rtn as Float: #^ x / #^ y

  defines program

    TryFinallyDemo()
      stdout <- Stdout()

      //try/finally without catch — cleanup guaranteed
      stdout.println("Starting work")
      try
        result <- riskyCalculation(20, 4)
        stdout.println(`Result: ${result}`)
      finally
        stdout.println("Cleanup done")

      //try/catch/finally — full pattern
      try
        second <- riskyCalculation(50, 10)
        stdout.println(`Second: ${second}`)
      catch
        -> ex as Exception
        stdout.println(`Handled: ${ex}`)
      finally
        stdout.println("All finished")

Coming from another language?

Java: try-finally for cleanup, try-with-resources preferred. Python: try/finally, context managers preferred. Rust: Drop trait, no try/finally. Go: defer for cleanup. EK9: try/finally with optional catch.

Keywords: resource, finally, try, cleanup, guarantee, propagate, exception