[Lazarus] Controlling access to a method
DrDiettrich1 at aol.com
Thu Jan 31 01:01:04 CET 2013
Mark Morgan Lloyd schrieb:
> You are of course entirely right: from the POV of protecting against
> silly mistykes it's entirely adequate to have a validation parameter,
> even if it's not used for anything else.
If only one initialization is sufficient, the property setter can reject
any further changes, after the value has been set to something other
than "uninitialized". I use such protection frequently, for properties
which cannot be changed after initialization of an object.
> I was originally thinking about
> it from the POV of bare-metal protected-mode code, where you could
> explicitly bind a procedure to ring 2 thus protecting it from ring 3
This only defers the authorization problem, to controlling ring
transitions. You can introduce a global "RingLevel" variable, checkable
in every protected procedure. Then everything depends on controlling the
write access (for rights elevation) to that variable. IMO this doesn't
help much, since when a subroutine is allowed to increase the ringlevel
for one purpose, it will be allowed subsequently to call *all* other
protected subroutines as well.
Another idea: every creator of an object can keep the object private, so
that nobody else can access it. This is impossible for an TFrame, which
is listed in the public Controls and Components lists. In this case
another "lock" object can be used, known only to the creator and the
protected object/procedure, as a spoofing protection.
Or you use "private" or "implementation" clause visibility. Then only
code inside that unit can access such a variable or field.
More information about the Lazarus