On 4/16/23 22:30, Edward Catmur wrote:
>
> On Sun, 16 Apr 2023, 15:36 Andrey Semashev via Std-Discussion,
> <std-discussion_at_[hidden]
> <mailto:std-discussion_at_[hidden]>> wrote:
>
> No, scope guards *are* moveable. And I can imagine use cases that rely
> on them being moveable, like returning an epilogue from a function.
>
> auto start_transaction(transaction_data& tr)
> {
> scope_exit completion_guard([&] { tr.complete(); });
> tr.init_with_data_data(x, y, z);
> return completion_guard;
> }
>
> And regarding storage, here's another use case that makes use of a scope
> guard as a non-automatic object - program exit handlers.
>
> // At namespace scope
> scope_exit at_exit_guard([] { puts("Good bye cruel world!"); });
>
> Or make that thread_local to make it a thread exit handler.
>
> Those are both scope_exit, though, not scope_success or scope_failure.
> When would it make sense to return one of the latter two or to use them
> at namespace scope?

If you define it so that scope_fail is called when main() or a thread
entry function is left with an exception, it could be used for the final
cleanup before program termination. For example, collect a backtrace
before terminating or emit a critical message in the log.

Returning scope_success/scope_fail from a function makes sense in the
similar cases as shown above, but when you want separate actions on
success or failure (or just one of them).