On 09-11-2011 11:33, Jonathan M Davis wrote:
On Tuesday, November 08, 2011 21:51:46 Davidson Corry wrote:
OK. Not addressing Alex's objections at all, it's not clear to me why
anyone would *need* to test the invariant of an object.
I wouldn't expect it to be something that you'd need to do very often.
However, if you give access to the member variables in your class or struct -
either directly or indirectly - allowing code outside the type to modify that
type's state, then the invariant can be violated. Now, it's arguably bad
design to allow such access when using an invariant (if not in general), but
it _is_ a case where the invariant can be invalidated.
- Jonathan M Davis
I do think Good Practice (TM) dictates that you shouldn't expose
something as mutable if mutating it violates the object's invariant.
Instead, you should use a property with preconditions.
In light of this, I can actually see why assert(obj) testing the
invariant can seem very, very odd. (And I mean, nobody's going to write
assert(this) or something like that...)
- Alex
