How to choose migration path from Delphi 2007_问答_开发者

I'm working with a team for a bigger application with Delphi 2007. It use a bigger legacy framework to access the data. Both the app and framework use String as datatype for strings. I have started to modify the code in framework to support Delphi 2009 strings, see my previous questions about this.

I see 2 alternatives now:

Alt 1 - Continue to use string as before. This is probably the cleanest solution as the framework will then supports Unicode. But the code in framework must be modified a lot to make this working. This require in depth understanding of the internal algorithms in framework. It is also a bigger chance to introduce new bugs.

Alt 2 - Replace String with AnsiString and Char with AnsiChar. This is propably a much easier solution and also how I start to modify the code (but then I start thinking and ask this question...). The negative side of this is no support for Unicode. Unicode support is not a requirement as it worked before but is nice to have. It could also be useful in the future. Another problem is that the application must send Ansistring variables as parameters in the methods for the framework instead of String as before. There are thousands of calls to change...

So I don't know right now. Both options require a lot of work, but Alt 1 is probably more risky and time consuming. What I want from this forum is feedback and comments as I guess I am not the first who have this problem.

EDIT Another issue is the memory footprint. I wrote a quick test that allocate an array of one million strings. Each string was filled with 26 chars from A to Z.

With Delphi 2007 it took 40.011.600 bytes and the time was 4:15 minutes. With Delphi 2009 it took 72.015.580 bytes and the time was 4:45 minutes.

The memory consumption was measured with GetHeapStatus.TotalAllocated.

I don't think we can afford to have the strings allocate twice as much memory.

I开发者_运维问答t is not unusual to have 500 MB in memory consumption for each client now. I guess much of this are as strings. Propably we try to use AnsiString as much as possible.

Regards

Either stay with the old version of Delphi, or go all the way. You'll have to sooner and later anyway.

Note that the "replace everything with ansistring" scheme is also not entirely foolproof, specially if you touch streams and your fileformats need to stay the same. There are no explicite TStringlists,tstringstreams etc with ansistring anymore.

The same probably goes for Datasnap, Indy and other frameworks.

You can try to use this trick for certain string intensive parts at first, to avoid changing too much code directly. E.g. I had an own XML library, which I patched to remain mostly ansistring. The library was only used sideways, and unicode was of no importance to it.

Start with "alt 2", then gradually add unicode support to your framework, then move over to Unicode.

Rationale: you want a stable app; switching over to Delphi 2009+ will eventually require you to really support Unicode.

Edit: 20100125

While doing "alt 2" watch the Delphi compiler hints warnings.
The situation that Andreas describes will generate such hints and warnings.

I have explained this in my CodeRage 4 session about Unicode and other encodings.
The above link points to a page where you can view the replay of that session.

If you still have questions, just drop them here.

--jeroen

We evaluated the transition 2007 -> 2009 a year ago and tried a a smaller project (200k lines). The result was that everywhere where you do not use "fancy" things like pointers, set of char etc the porting is really not that difficult . Especially the GUI units we're ported within a day or so. This is equivalent to opt1.

The library units with low level routines, access to measurement systems etc etc was a whole different story. Here we choose to translate string -> ansistring, char -> ansichar etc etc. Porting these units is a pain to get correct and the customer won't pay for the transition. Hence opt2 for those units.

This mixed method gave us best of both worlds but we will keep some larger projects at Delphi 2007 and probably only port when a 64 bit version of the compiler will come out.

It'll be more work, but I'd really recommend that you upgrade to Unicode strings, because that's the native string type of the VCL and so all your controls will be dealing with Unicode strings anyway. Trying to convert everything back and forth will cause you all sorts of hassles.