Re: Variables in for loop (style issue)
Lourens Veen wrote:
On Tue, 23 May 2006 17:49:14 -0400, Thorsten Ottosen wrote:
Well, there seems to be several views on encapsulation:
1. you don't know/care what data members the class has
2. you can't modify the class' invariant without using a member
function
The first is of minimal importance, the second is of *immense*
importance.
There is quite some misunderstanding in academia
and in general anout the virtues of encapsulation.
(Partly because people don't understand what a class invariant is).
Maybe I am one of those people who doesn't understand what a class
invariant is, but isn't the point of class invariants that they _always_
hold?
As David pointed out, my wording was a bit imprecise. A class invariant
of type T is static. An object's constructor and member functions must
leave the object in a state where the class invariant (of the type of
the object) holds.
You can not modify them using a member function, because they are
part of the definition of the class.
Giving direct access to class internals may (depending on the nature
of the class) allow outside entities to modify the state of an object of
that class in a manner inconsistent with the class invariants, thus
putting it into an invalid state.
Right.
To prevent that, we hide (encapsulate) these internals, and only expose
operations (member functions) that modify the internals in a manner that
is consistent with the class invariants, thus ensuring that any
object of
that class remains in a valid state at all times.
Right.
However, note that "hide" is different form "encapsulate", as I try to
point out above. It's the least important property of encapsulation.
-Thorsten
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