Invariants are useless the way they are defined

[deadalnix]

As they are defined now, invariant are plain useless. I find 
myself disabling them one by one in my code as soon as cases get 
outside simple trivia.

The problem is that invariant are checked at the beginning/end on 
public function calls. As a consequence, it is impossible to use 
any public method in an invariant.

For instance, just right now I did refactor a struct to use 
bitfields, in order to make it more compact. Now I have to remove 
the invariant as field access are now function calls.

Another typical situation is when you want to assert certain 
properties in a class hierarchy, where calling virtual method is 
part of the invariant check.

invariant should (and must to be useful) be inserted at callee 
point, when the callee isn't itself subject to invariant 
insertion, and around public memeber manipulation (when the 
manipulator isn't subject to invariant insertion).

Any other pattern it doomed to create infinite recursion for non 
trivial invariant checks.