e.rs

> cargo run --example deferred
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/examples/deferred`
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', ../src/libcore/option.rs:317
stack backtrace:
   1:        0x10f196bea - std::sys::backtrace::tracing::imp::write::h4b09e6e8c01db097
   2:        0x10f198baf - std::panicking::default_hook::{{closure}}::h1d3243f546573ff4
   3:        0x10f198015 - std::panicking::default_hook::h96c288d728df3ebf
   4:        0x10f1985c6 - std::panicking::rust_panic_with_hook::hb1322e5f2588b4db
   5:        0x10f198464 - std::panicking::begin_panic::hfbeda5aad583dc32
   6:        0x10f198382 - std::panicking::begin_panic_fmt::h4fe9fb9d5109c4bf
   7:        0x10f1982e7 - rust_begin_unwind
   8:        0x10f1c2cf0 - core::panicking::panic_fmt::h4395919ece15c671
   9:        0x10f1c2bf4 - core::panicking::panic::hc74ff52ed78364e1
  10:        0x10f1991ab - __rust_maybe_catch_panic
  11:        0x10f197b56 - std::rt::lang_start::haaae1186de9de8cb
  12:        0x10efb9359 - main
fatal runtime error: failed to initiate panic, error 5
error: Process didn't exit successfully: `target/debug/examples/deferred` (signal: 6, SIGABRT: process abort signal)