On Mon, Aug 11, 2014 at 4:52 PM, Christian Stimming <christ...@cstimming.de>
wrote:
> Hi Aaron,
>
> thanks for investing time in Gnucash and also in its development towards
> more
> future-proof programming technologies.
The pleasure is mine.
> I was a bit puzzled about the benefit
> of switching the "normal compiling" from C to C++, just by itself. IMHO,
> there
> is of course an immediate benefit if the data structures move from plain C
> structs to C++ classes, with constructor/destructor and such. If you plan
> to
> do such a transition with any of gnucash's data structures, of course every
> code using those will have to be C++. However, just changing this into C++
> doesn't also solve the problem here: The usage of the C structs in the
> code is
> just that: C structs, with foo_new() and foo_delete() functions and maybe
> even
> glib's reference counting. To really use C++ classes instead, every single
> usage of those old C idioms will have to be replaced by proper C++
> constructs.
> IMHO, "just" switching the C compiling to C++ doesn't quite bring you much
> gain here. Do you think it helps you much?
Thanks for asking! You're right, changing the compiler from gcc to g++ does
nothing to directly improve maintainability or performance of the code in
question. As I see it, the gains come after that painful process. I'll go
ahead and repeat the strategy I'm investigating for reference:
1) Make all code compile as c++ code
2) Add poison to make it idiomatic c++ code
3) Make higher level changes
Part of the strategy includes this plan being followed rather strictly.
Using this plan, step 3 brings with it the possibility of converting
interfaces to c++ (giving classes constructors and destructors, making
templated algorithms, etc.). Currently, for instance, the guid object is
not usable as proper c++ code even if there were a client code file that
could take advantage of it, because there is no c++ interface in the header
file; if there were, all the C code would barf at compile-time.
> [...snip...] I see some more
> benefit when changing individual data structures to C++, then switching the
> old C functions into wrappers that make the new C++ behaviour available to
> the
> C side.
In a way, that's just what I'm going for. The only way to make typedef
struct _gncGuid {...} GncGUID; into class GncGUID; is to make sure that
every compilation unit (which uses GUID) knows what "class GncGUID;" means!
At that point, it would be no problem to make GncGUID a class (or a typedef
for a boost class), and even manage it with smart pointers or whatever.
This can be done right alongside (for example) the existing glib date
interface. With this kind of change, we're freed from the requirement that
each code file communicates with the other code files "in C". We are now
free to speak a different language as we desire, as we are able, and,
importantly, at our liesure.
> This means the existing C code can continue to compile in C, and the
> next steps would rather be to open the possibility for new C++ code such as
> unittests and maybe new GUI code in C++ (or python or something similar).
So it sounds like you're talking about introducing new c++ code that uses
the existing C interfaces, which I think is an obvious win. The next win
that I'm striving to see is the existing C code start to use C++ idioms,
data structures, etc.
It would be nice if all that makes sense, but I know better than to even
hope for that :-). Thanks again for asking, and please help me clarify by
asking more questions!
In Christ,
Aaron
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