Re: [boost] [contract] move operations and class invariants

Subject: Re: [boost] [contract] move operations and class invariants
From: Peter Dimov (lists_at_[hidden])
Date: 2017-11-29 14:15:16

Lorenzo Caminiti wrote:

> C++ requires that moved-from objects can still be destructed. Because 
> contract programming requires class invariants to hold at destructor 
> entry, it follows that moved-from objects must still satisfy class 
> invariants.

No, moved-from objects must be valid objects. Not only can they be 
destroyed, they must be usable. Their state is unspecified, but invariants 
hold.

> That sounds restrictive... and it might force the class invariants to be 
> empty. For example, for vector a class invariant is size() <= capacity(). 
> Should that sill hold after the vector has been moved?

Yes.

> That means I can still call size() and capacity() on a moved-from object, 
> which might not be the case.

No. You must be able to call size() and capacity().