I think its more of the realization that types are actually freaking useful for determining "provability" of a system. C++ perhaps takes it too far with Const, but it allows the compiler to prove that certain functions will not attempt to modify certain variables.
There is very little in terms of "provability" that either C++ or its types give you. Proving anything really interesting (for example, the absence of race conditions in concurrent code) still seems like pretty much an arduous process in languages not explicitly designed for such things.
Compared to Python or Ruby, you're pretty much relying entirely on culture and good habits to ensure the proper rules of encapsulation. Any code may modify the private members of your objects. (Granted, C++ has "mutable", Java has the whole "Reflection" loophole as well. But you can search for those edge cases rather easily).
That didn't seem very comprehensible to me, but if you're claiming that in Ruby, you can modify member variables of someone's objects, well, you can't, unless you use reflection as well (not only that, but the access to member variables is object-based, rather than class-based, so you can't access the member variables of an object from any other object, even if they are of the same class, unlike in C++ - so much for the "objects communicate by passing messages" in C++!). More to the point, in C++, you can always cast a pointer into something that makes the raw data accessible. There's enough stuff in C++ for you to blow your whole leg off instead of just shooting yourself into the foot.
Take for example, proper use of a unique_ptr<lock_guard<std::mutex> > in C++. You can pass around the unique_ptr, and guarantee that you are in "unique ownership" of a particular lock at compile-time.
In C++, you may not be able to prove "the lack of race conditions", but you can prove things like "I'm the only one who is holding onto this mutex right now" thanks to stuff like unique_ptr... which tracks that stuff. These primitive proofs are performed at compiletime, and have little-to-no effect on runtime as well.
Stronger languages with stronger type-systems (ie: Haskell) can prove / disprove which code has side-effects... because you've explicitly passed the Monad around. (Note: Code without side-effects is guaranteed to not have race conditions).
So yes, there are important things you can prove using the type-system. More importantly, it is the compiler's job to automatically conduct these proofs every compile cycle.
There is very little in terms of "provability" that either C++ or its types give you. Proving anything really interesting (for example, the absence of race conditions in concurrent code) still seems like pretty much an arduous process in languages not explicitly designed for such things.
Compared to Python or Ruby, you're pretty much relying entirely on culture and good habits to ensure the proper rules of encapsulation. Any code may modify the private members of your objects. (Granted, C++ has "mutable", Java has the whole "Reflection" loophole as well. But you can search for those edge cases rather easily).
That didn't seem very comprehensible to me, but if you're claiming that in Ruby, you can modify member variables of someone's objects, well, you can't, unless you use reflection as well (not only that, but the access to member variables is object-based, rather than class-based, so you can't access the member variables of an object from any other object, even if they are of the same class, unlike in C++ - so much for the "objects communicate by passing messages" in C++!). More to the point, in C++, you can always cast a pointer into something that makes the raw data accessible. There's enough stuff in C++ for you to blow your whole leg off instead of just shooting yourself into the foot.