iilyak commented on PR #5576:
URL: https://github.com/apache/couchdb/pull/5576#issuecomment-2997570293
> > Handling flag doesn't land naturally into maybe pattern.
>
> Also handling error cases would be tricky if flag aware implementation is
attempted in the `handle_call({write_header, Bin, Options}, _From, #file{fd =
Fd, eof = Pos} = File) ->` clause. Since in this case I would need to
distinguish error from sync (where I need to stop the gen_server) from errors
from `file:write`. The problem is that both errors has same form `{error,
Reason}`. So I have to split out the helper function anyway.
>
> I'll keep thinking about how to implement `sync` flag. However so far it
seem more complex than version with dedicated function.
This is the ugliest hack (which I am against myself) for two reasons: 1) use
of `if` which is not newbie friendly, 2) use of `{expr}` to make shape
different.
```erlang
ShouldSync = true,
maybe
ok ?= (if ShouldSync -> fsync(Fd); true -> ok end),
{ok} ?= {file:write(Fd, FinalBin)},
ok ?= (if ShouldSync -> fsync(Fd); true -> ok end),
{reply, ok, File#file{eof = Pos + iolist_size(FinalBin)}}
else
{{error, _} = Error} ->
{reply, Error, reset_eof(File)};
{error, _} = Error ->
% We're intentionally dropping all knowledge
% of this Fd so that we don't accidentally
% recover in some whacky edge case that I
% can't fathom.
{stop, Error, Error, #file{fd = nil}}
end;
```
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