[Development] QFile: writing via a temporary file

[David Faure]

On Friday 06 January 2012 10:24:04 Craig.Scott at csiro.au wrote:
> I like the idea that if nothing goes wrong, then close() commits the changes
> (ie renames the temporary file to the real file name). It makes using a
> QFile with this feature very transparent and means that functions that
> accept a QFile will continue to behave in the way they did previously
> regardless of whether or not this feature was enabled for a given QFile
> instance.

This is an excellent point, I'm convinced now.

> If something goes wrong during the write and you want to discard the file
> contents you've written out so far, remove() doesn't seem to convey that
> concept. I would prefer to see a function name that makes things clearer,
> such as discardChanges() or similar.

Excellent point too. Much clearer indeed.
Yay, I love this.

Note that remove() would still work, too: if it removes the temp file, then it 
also means discarding any changes. But that would be a side effect, 
discardChanges() would be the proper API for doing it.


Now there's just one question remaining: even if the rule is that all 
operations apply to the temp file, between open and close... what should 
QFile::fileName() return? The temp file name, to obey that rule, or the target 
file name, for symmetry with setFileName()?

I'm tempted to say: the latter, because the temp file is really internal, and 
to prevent surprises (breaking symmetry with setFileName). Of course it means 
file.remove() won't be the same as QFile::remove(file.fileName()) anymore... :)

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Sponsored by Nokia to work on KDE, incl. KDE Frameworks 5