On Fri, Oct 26, 2012 at 9:06 AM, Peter Kasting <[email protected]> wrote:
> On Fri, Oct 26, 2012 at 8:27 AM, Rik Cabanier <[email protected]> wrote: > >> It is valid for a const method to return you a new object ie a const >> factory object. >> In that case, const-ness would not be desired. >> > > Not really. The point of this thread is that such functions may not > modify an object's state themselves, but they vend access that can be used > by the caller to modify it. > > Consider for example: > > Child* Parent::getNewChild() const; > > Assuming the Parent doesn't have a list of its children (questionable), we > can implement this without mutable pointers. But then a caller can do: > > Child* child = parent->getNewChild(); > child->parent->mutate(); > this would only be possible if that parent object is casting away a 'const' somewhere or accessing a global non-const object. Maybe there should be a rule that 'mutable' or 'const_cast' should not be allowed. > > If you generalize this you find there are very, very few cases where a > const object can vend a non-const pointer that cannot possibly be used to > change the state of the world the const object sees. Which is why the rule > of thumb suggested in this thread is safer and easier than trying to reason > about individual cases. > > PK >
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