Board index » delphi » Tricky Question about howking constructors

2005-02-10 12:28:42 AM
delphi164
Hi,
I've been giving the following idea some thought but I'd really
appreciate your insights.
I coded an OPF. Instead of objects the programmers uses proxys that
contains the real subject. To create a new object inside the framework (and
persistent) you use a Factory. Something like this:
var
aClient : TClient
Begin
aClient := HecFactory.CreateNewClient;
..
Here a Client actually references a ClientProxy but that is supposed to be
"transparent" to the programmer.
The thing is like this. I managed to hook the constructor using some
libraries that modifies the assembler in memory or something. Using those
libraries I can make something like:
Client := TClient.Create;
But when you see the client Classname it result that it is actualy a proxy.
In that way the creation if even more transparent. You can add a unit to
your project have persistent objects and comment that unit and the code
would still work.
I tested troughtly and it worked perfectly but...The ting is. To do that
you hace to modify de ASM in memory with this libraries.
I have to decide if I hace to implement it or leave the factory as it is.
What is your advice. The procedure to do it is very strange so I cannot make
my mind.
I hope I explained my point. If I missed something or if there is some
detail missing please ask.
What is your advice?
Esteban Calabria
 

By the way...
What I did is something similar (in result, not in method) to overriding the
ClassLoader in Java.
 

Hechicero writes:
aClient := HecFactory.CreateNewClient;
or do some "magic" asm stuff to enable code like:
Client := TClient.Create;
?
Use the factory! It is more powerful because you can have multiple
implementations of the factory, one factory returning proxies, another
returning the "real" objects, so it is just as transparent (and is a
common pattern). The asm alternative sounds *very* ugly. :-)
Cheers,
Jarle
 

In article <420a46b3$XXXX@XXXXX.COM>,
XXXX@XXXXX.COM says...
registry'. We have a generic for it, and it works like a top:
const
MARSHAL_HEC = 'hec_marshaller';
CODE_PAGE = 'code_page';
MarshallingRegistry.AddFactory(
MARSHAL_HEC,THecMarshallerFactory.Create);
...
Kind := MARSHAL_HEC;
Configuration := TConfiguration.Create;
Configuration.Add(CODE_PAGE,CODE_PAGE_SPANISH);
Marshaller := MarshallingRegistry.Build(Kind,Configuration);
-- Ritchie Annand
Senior Software Architect
www.malibugroup.com
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