C++ work

Ted Creedon tcreedon at easystreet.net
Wed Sep 10 08:05:06 EDT 2014

mark up the screenshots with proposed changes

then write the user's manual, systems administrator's manual & systems
administrator's reference manual - submit for comments & approvals

then write C++ header files that wrap your subroutines &compile & link

only then can you begin code conversion

writing code is the last step, not the first step - and its very boring-
but you do get zero defect code

retired senior project manager
Tektronix Research Labs

On Tue, Sep 9, 2014 at 2:50 PM, John Ralls <jralls at ceridwen.us> wrote:

> On Sep 9, 2014, at 2:24 PM, Geert Janssens <janssens-geert at telenet.be>
> wrote:
> > On Tuesday 09 September 2014 15:12:33 Aaron Laws wrote:
> >> The short question is: What GUI framework is gnucash likely to target
> >> in c++?
> >>
> > Equally short answer: likely Qt or WxWidgets. But we never did a
> detailed evaluation yet.
> >
> >> I've heard it mentioned that the current framework (GTK?) doesn't make
> >> sense in c++ because it's so gobject-oriented, but I didn't hear
> >> anything else suggested. I know there's a QT effort which seems like
> >> a reasonable way to go, but haven't heard it actually endorsed
> >> anywhere.
> >>
> > Exactly
> >
> >> Currently, c++ work is starting at the deepest point (the part of the
> >> code that is relied on by everything), qof, so that a C api has to be
> >> maintained until everything that relies on QOF has a way of accessing
> >> the c++ interfaces. This means that c++ and C interfaces need to be
> >> created and maintained in parallel until everything's ready to
> >> switch. This has grated on me for quite a while, but I see it as a
> >> very difficult problem. I don't see a quick way to fix it. I've tried
> >> (and technically succeeded ^_^) compiling the whole project as c++,
> >> but that's not so great because the dynamic linking doesn't work
> >> because of mangling. Repairing this solution doesn't seem like a
> >> profitable way forward. It's sort of like throwing all your
> >> belongings into a river, then swimming across yourself, and trying to
> >> collect everything on the other side, making sure you didn't lose
> >> anything.
> >>
> >> Another way that I've been trying to consider is to start on the part
> >> of project upon which nothing relies. That way, that part of the
> >> project can be completely C++. Then, take the next thing which
> >> doesn't expose a *used* C api. Rinse and repeat. This way, there will
> >> never (?) have to be a duplicated API in any system.
> >>
> > Sounds nice in theory. I fear it will be equally if not more difficult
> than the current approach
> > though.
> >
> > Taking your example of first replacing the gui.
> >
> > As you bring up yourself it is heavily gobject based. And in addition
> the controller, model and
> > view code are mixed up. Rewriting it in (say) Qt, means it will now use
> Qt objects. But the
> > "business logic" (our engine code) is still gobject based.
> >
> > So now in order for the gui to talk to the business logic you have to
> create an interface layer
> > between the engine and the gui that will do the proper translations
> between the two object
> > models. That is probably more work than maintaining the existing C api
> in the path currently
> > chosen.
> >
> > In addition logically it doesn't make sense to start from the gui and
> drill down to the model.
> > Your gui should be based on the model and controller logic so it only
> makes sense to start there.
> > Going the other way around as a sure way to make wrong assumptions about
> how the lower
> > layers will be implemented and in the best case mean several revisions
> to the higher layers or
> > having to start over in the worst case.
> >
> >> Another way to think about this is as a tree structure. I'll throw
> >> something up, and I'll eagerly await corrections! Read "->" as "relies
> >> on":
> >>
> >> GUI (GTK?) -> Business Logic
> > So rewrite the gui and an interface layer between the two
> >> Alternate gui (WEB?) -> Business Logic
> > Same here.
> >> GUI (GTK?) -> Reporting Infrastructure
> > Same here.
> >> Business Logic -> QOF
> > Rewrite the business logic and write an interface layer between the two.
> > Oops, the way we write the business logic now means we need to change
> the gui layer, because
> > it made some invalid assumptions on what the business logic would be.
> > So rewrite the gui here as well
> >> Reporting Infrastructure -> QOF
> > Rewrite the reporting infrastructure and write an interface layer
> between the two.
> > Oops, the way we write the reporting infrastructure now means we need to
> change the gui
> > layer, because it made some invalid assumptions on what the business
> logic would be.
> > So rewrite the gui here as well
> >
> >> QOF -> libdrm, etc.
> > Rewrite qof and realize we end up with a different implementation that
> we thought we would.
> > So rewrite the business logic and the reporting infrastructure once
> more. And bollocks, that kills
> > our gui design again. Rewrite the gui...
> >
> >>
> >> So, if QOF is changed, it still needs to support Business Logic with a
> >> C api until Business Logic is changed which can't happen until all
> >> GUIs that rely on it are changed. If, however, a gui layer is
> >> changed, that's all there is to it; there are no dependencies (if
> >> there are, we should have started at the dependency!). Once all GUIs
> >> (I know there's only one, but I'm trying to create a sufficiently
> >> complicated example!) are c++-ready, the Business Logic can be
> >> converted. No redundant API is necessary.
> >>
> > See my worst case but not unlikely scenario above. I predict much more
> work when working top
> > down because it's impossible to rely on a lower level interface if the
> implementation hasn't
> > been done yet.
> What Geert mentioned in passing but left out of his discussion is that
> there’s a lot of business logic code mixed into the GUI code. That has to
> be teased out and separated so that the model stuff goes down into the
> engine where it belongs and the stuff that’s just computation for display
> or input goes into some middle classes in separate directories, and the GUI
> directories contain just the code which describes the GUI itself, calling
> the controller classes as they need.
> The pushing the model stuff down into the engine part of that job makes
> the most sense to do when the engine is migrated, but the extracting part
> could be done now. In fact having the pieces clearly separated ahead of
> time would make it easier to define the engine API when the time comes.
> And oh-by-the-way, there’s also some GUI that’s still in scheme and has
> business logic in it that the C parts of GnuCash can’t see at all. That
> also needs to get pulled apart into the appropriate MVC layers.
> All of that aside, there’s a fundamental flaw in your reasoning. If you
> write a new C++ GUI, even if there wasn’t an MVC separation issue, all of
> the controller calls would be to C functions, because that’s what the
> controller layer if it existed would be written in. It would in turn be
> calling C functions in the model layer, because that’s what the engine is
> written in. So even if nothing changed, you’d still be in the position of
> rewriting each upper layer over to operate on C++ objects instead of
> GObject objects as you drill down. Everything would be done twice as a
> *best* case.
> Regards,
> John Ralls
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