11_defer_errors.li

// Deferred blocks run on normal return and exceptional unwind.
let events = []

fn divide(numerator, denominator) {
   defer { events::push("leave divide") }

   if denominator == 0 {
      throw "division by zero"
   }
   return numerator / denominator
}

assert(divide(12, 3) == 4)
assert(events::len() == 1)
assert(events[0] == "leave divide")

let caught = nil
try {
   divide(12, 0)
} catch error {
   caught = error
   events::push("caught error")
}

assert(caught == "division by zero")
assert(events::len() == 3)
assert(events[1] == "leave divide")
assert(events[2] == "caught error")

// Multiple deferred blocks in one scope run in last-in, first-out order.
fn nested_cleanup() {
   defer { events::push("first defer") }
   defer { events::push("second defer") }
   events::push("body")
   return 42
}

assert(nested_cleanup() == 42)
assert(events[3] == "body")
assert(events[4] == "second defer")
assert(events[5] == "first defer")

print("defer and errors: ok")