[fpc-pascal]Classes/Objects/Pointers / Pointer Help
anton.tichawa at chello.at
Mon Feb 10 13:24:05 CET 2003
If TNick is a class - I don't have the declarations - it must be initialized
nicks := new(TNick, init(nick, hops, signon, ident, host, server, unused,
That's correct because TNick is already a pointer, not an object, and init is
required to call TNick's constructor.
But the problem ist a more generic one .. I'll try to formulate the
questions: A procedure (Alice) passes Data to another procedure (Bob):
1. is Data "empty", i. e. is the call to Bob parameterless? Note that even in
this case, there is still information flow between them, because 1. Bob knows
having been called by Alice (which is information > 0 bit), and 2. might read
input and return results in a predefined, global manner.
2. is Data readable?
3. is it writeable?
4. is it a special (CPU, hardwre) register, or global memory?
5. Is Data the only one of it's kind, or does it need addressing? If it needs
addressing, is the address defined? Does Data have a fixed size? If not, is
the size known or unknown?
6. Other questions that I don't see at the moment. One of these is the SWITCH
7. Is Data a pointer? If this is the case, then pointer types should be able
to point to "null", "readable", "writeable", "register / memory", and other.
I think the solution isa kindof redundancy. As a legacy example, look at
pointers: Pointers with value $00000000 are defined as "nil". That disallows
pointing to a variable at address 0. On one hand, that excludes memory at
address 0 to be used for "pointed-to" data. On the other hand, low-level
access with references to address 0 might still be required in some cases,
simply to increase performance.
There should be some kind of aggreement about Data. As a second example,
Classes e. g. are now checked (the VMT contains a kind of checksum), but this
is dangerous for every-day run-time type information, because a pice of
arbitrary data might contain a correct checksum, thus pretending to be a
class .. trak! exception.
I suggest the words "SAFE" and "FAST" for these two "modes of operation".
SAFE mode obeys legacy agreements, forces redundancy, and Bob is guaranteed
to find a solution for the questions mentioned above, converning Data. In
case of misunderstandings, exception handling moves the system to the safe
In FAST mode, there is no redundancy, i. e. hardware runs at full speed, but
software might crash.
I suggest a BIG RED SWITCH on top / front of the computer, which is normally
switched OFF, forcing SAFE mode, disallowing references to address 0 with a
pointer, requiring action to follow previous negotiations.
Any ideas how to continue this topic?
"Adas Methode war, wie sich zeigen wird, Tagträume in offenbar korrekte
Doris Langley Moore: Ada, Countess of Lovelace (London 1977).
Volkertstrasse 19 / 20
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email: anton.tichawa at chello.at
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