Il 22/07/2012 10:39, Michael Van Canneyt ha scritto:
On Sat, 21 Jul 2012, Florian Klämpfl wrote:
Am 21.07.2012 23:06, schrieb Ivanko B:
No, just reorder the fields so that they can be properly $IFDEFed as
protected for nonLAZARUS and left (private) as is otherwise.
Why should lazarus people have less chances to mess with private fields?
Either we make them public for all or for nobody. Of course, then
everybody has to take care of the fact that users might mess with these
fields.
Which is exactly why we will not do this.
The base classes expose a well-defined API. This API is a contract you
make with the developers of descendent classes.
Some fields are kept private to ensure that the terms of the contract
can be met. Making them public/protected means that the terms of the
contract can be broken by Developer A, when the code of developer B
depends on the terms being rigorously enforced, and his code can go
very wrong.
This is of course not so for all private fields, which is why I ask
for reasons, so I can decide for each field what can or cannot be done.
There are excellent reasons not to expose private fields. What must be
opaque and what must be visible to end users are designers decisions
which involve the capability of providing new implementation without
breaking existing code, take into account multiplatform needs, consider
the planned improvements, etc. etc.
On the other side there are sometimes good and sound reasons for someone
to break this rule, at his own risk, of course. It may be to quickly fix
a bug, to provide an extra feature by reusing an existing object instead
of rewriting a lot of code, etc. Of course this is a practice not to be
recommended in general, but it occurs. And in many cases it is connected
to specific needs which aren't of general interest, making the effort of
supporting them hardly worthwhile.
IMHO a clean solution can be found at language level: if I declare
TMyclass = class(TWhatever)
then I just get the degree of visibility that the class designer has
decided.
But if I declare (just an example, a better keyword can be found)
TMyclass = subclass(TWhatever)
then I get full visibility, all the private fields of TWhatever become
just protected in TMyclass, and of course, I'm on my own. The designer
is not bound to any contract, because I have explicitly decided to run
the risk.
This solution would allow mainstream designers to keep fields visibility
to what they deem to be a safe level in general, without making it
impossible to non mainstream designers to provide features which aren't
considered of general interest.
Just my 5 cents.
Giuliano
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