Objects question..._(re)

Thu, 4 Sep 1997 09:34:58 +0200 (MEST)

According to Orlando Llanes:
> 
>     I'm curious about something with objects as it will affect the game lib.
> What I need to know is how objects work at run-time.

Each instance of each object has an implicit "vmt" field which
contains a pointer to the "virtual method table" where the addresses
of all virtual methods are stored.  GPC produces inline code to
initialize the vmt immediately before a constructor is called.
(BP does the assignment inside the constructor instead.)  When a
virtual method is called, the program dereferences the vmt field,
and so on.

> Is there a way to
> create an object so that it will be loaded only if allocated with "New"? In
> other words, is there a way to keep the code for the object on disk until
> it's needed, and removed form memory when not?

Write a constructor that fetches all needed data from the file when
the object is `New'ed; if you want to keep the stuff in the file
current, write a destructor that writes everything back to disk
when the object is `Dispose'd.  (* BTW, this has nothing to do with
the internals how objects work at run-time. ;*)

You are obviously writing a memory manager to keep the amount of RAM
your program uses small and to use the disk instead.  On UNIX-like
platforms you don't need to do this because the operating system does
it for you.  Just allocate as many MegaBytes as you need; if this
exceeds your physical RAM the operating system swaps out the unneeded
parts automatically and restores them when they are needed again.
Your application does not even notice this.

Have fun,

    Peter

 Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer
peter.gerwinski@uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201]
 maintainer GNU Pascal [970714] - http://home.pages.de/~gnu-pascal/ [970125]

Peter Gerwinski (peter@agnes.dida.physik.uni-essen.de)