Re: Class invariants and implicit move constructors (C++0x)

On 15 Aug., 06:07, Scott Meyers wrote:


Yes, I think so. Thanks for pointing out this example. Actually, I've
recently written a class with a member of type vector<deque<float> >
where I also keep track of the minimum deque length and how many
deques have this minimum length. But I don't check this invariant
prior to destruction so it would only fail if the moved-from object is
still used without any kind of "re-initialization".

I guess the important question is: Are these tolerable corner cases?

Under the current rules, a solution for your example doesn't require
writing your own move operations or deleting them. It could look like
this:

  class Widget {
  public:
    ...
  private:
    std::vector<int> v1;
    std::vector<int> v2;
    mutable std::size_t cachedSumOfSizes;
    mutable replace_on_move<bool,false> cacheIsUpToDate;
    ...
  };

where replace_on_move<bool,false> is a class that wraps a bool and
sets it to false when it is moved from. I guess such a class template
would come in handy.

Cheers!
SG