Phil/Max
Would it be possible to build up a VMT translation
table? as unidentified objects are passed to the dll it
could built a table of names and parents, at least this would
incrementally get faster
Neven MacEwan (B.E. E&E)
Ph. 09 621 0001 Mob. 0274 749062
Phil Middlemiss wrote:
Thanks Max, I guess I'll stick with what I have....
Cheers,
Phil.
----- Original Message -----
From: "Max Nilson" <[EMAIL PROTECTED]>
To: "'NZ Borland Developers Group - Delphi List'" <[EMAIL PROTECTED]>
Sent: Thursday, September 09, 2004 10:02 AM
Subject: RE: [DUG] Passing Objects to a DLL
Phil Middlemiss asked:
Thanks Max, I thought it was something like that, but didn't
know the specifics. BPL's are out of the question for us...
we looked at that and ruled it out earlier since the
versioning nightmare is even worse than with DLL's. Is the
BPL the only way around it?
I've looked at the code concerned, _IsClass and _AsClass in System.pas
that
implement 'is' and 'as' to support the compiler, and the only fix I can
think of is exactly equivalent to the solution you already have.
Anyway what you could do is runtime patch the _IsClass and _AsClass (plus
optionally TObject.InheritsFrom) routines to perform a jump into
alternative
code that does the same walk up the VMT parent poiner list, but compares
by
name rather than VMT pointer.
But apart from that the entire Delphi object supprt code is based on the
concept of an object being a a point to a block of memory, the first 4
bytes
of which are the pointer to the objects VMT. The only possible way to
intercept this behaviour would be to hack TObject.InitInstance to create
objects instances with the VMT pointer set to the EXE's VMT rather than
the
DLL's VMT. To do this you would need to export some sort of help function
from the EXE that could return the VMT pointer for a named class and use
this in the DLL's.
Cheers, Max.
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