An issue I encountered in D1 with invariant is using delete: I have a
method that deletes the current object, and obviously then any
invariant would fail.
It would be nice to have a way to disable invariant in that case.
In D2, as delete is not allowed anymore (if I got it correctly) this
is not a problem.
Fawzi
On 27-ott-10, at 15:08, Stanislav Blinov wrote:
27.10.2010 4:00, bearophile wrote:
I have not asked this in the D.learn newsgroup because I think it
may be a bit interesting for other general people too.
In D contract programming the invariant is not called before/after
private methods. I think that in some cases you may want to disable
the invariant even in some public methods. If your class/struct has
a public method that invalidates the state of the class instance,
and one public method that fixes the class instance state (I am
thinking about certain data structures where in a first phase you
may add many items, and then you ask the data structure to clean up
itself and become coherent. This may avoid some computations), I
have found this way to implement it:
If I get this right, then it is by design that your class may have
several general logical states: e.g. "initializing" and "coherent".
Given this, I don't see why you'd want to disable invariant checks
rather than modify those checks instead to validate current logical
state. In fact, that "ghost" field simply serves as a flag for
invariant showing which logical state it should enforce. The fact
that states are 'logical', e.g. are different while represented by
the same physical fields doesn't always rule them out as, uh, class
states: you could as well have two separate inner classes that
perform initialization and polishing, each with its own invariant.
Then you could use those inner classes' private methods (without
causing their invariant checks), but in main class' invariant
perform an assert on them to ensure their state is valid.
IMHO, proper invariants should be strict and act by the numbers at
all times, otherwise there's little to no gain in using them at all.
