[fpc-devel] Interface scope incompatibility with Delphi

[Graeme Geldenhuys]

Hi,

Attached is a simple console application that outputs a hierarchy of log
information. Under Delphi 7 we used to use a TInterfacedObject descendant
to track the call stack. This same trick was very handy for changing and
restoring the mouse cursor too.

When you create an instance it logs entry information, and increased the
indentation level. When that interface instance went out of scope in
decreased the indentation level and logs exit information.

Unfortunately this doesn't have the same affect under FPC (tested with
Windows and Linux).

The problem is that under FPC, the Interface instances immediately goes out
of scope. It seems Delphi held on to that instance even though you did not
store it in a variable. Once the current procedure/method is complete, then
only the Interface instance went out of scope.

Why do I need this:
-------------------
  * Delphi compatibility of course ;-)
  * Due to the bad state of debugging under FPC[*] I am implementing
    (actually just extending the thread cached log-to-gui class of tiOPF)
    to recreated a product similar to Raize Components's CodeSite product.
     http://www.raize.com/DevTools/CodeSite/Default.asp

http://www.ackerson.us/AckersonSoftware/Dev/CodeSite/CodeSiteEx/method_tracing.html
  * Allows for easier profiling like in 'fpprofiler' project. The
    CodeSiteEx product does this as well.
     http://www.ackerson.us/AckersonSoftware/Dev/CodeSite/CodeSiteEx/timer.html


Can anybody shed some light on why this doesn't work in FPC, and if it is
possible to make FPC delphi-compatible in this regard?



Delphi 7 app output:
--------------------------------------
Y:\tests\logger>Project1
>> Main
  Here I am
  >> TryMe
    i = 42
    42 is the answer to everything
  << TryMe
  We are reaching the end
<< Main
--------------------------------------


FPC 2.4.3 (Linux) app output:
--------------------------------------
logger $ ./Project1
>> Main
<< Main
Here I am
>> TryMe
<< TryMe
i = 42
42 is the answer to everything
We are reaching the end
--------------------------------------


FPC 2.4.3 (Windows) app output:
--------------------------------------
Y:\tests\logger>project1
>> Main
<< Main
Here I am
>> TryMe
<< TryMe
i = 42
42 is the answer to everything
We are reaching the end
--------------------------------------




Footnotes:
[*] - Inconsistent results between FPC+GDB under 32-bit and 64-bit
      environments.
    - DbugIntf unit can't keep up to fast logging under Windows, and
      simply looses debug information
    - Can't debug expressions via GDB
    - Can't debug something as simple as AnsiString's under GDB.
    - Can't debug a character index into a ansistring with GDB.
    ...the list goes one...



Regards,
  - Graeme -

-- 
fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal
http://opensoft.homeip.net:8080/fpgui/

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