Re: [boost] Interest in a protected pointer

Subject: Re: [boost] Interest in a protected pointer
From: Dmitry Goncharov (dgoncharov_at_[hidden])
Date: 2009-02-11 03:41:26

Ray Logel wrote:
>
> Is there any interest in pointer wrapper similar to scoped_ptr or 
> shared_ptr which can be used for pointer member variable which can the 
> referenced value can't be modified by non const functions?  This class 
> wouldn't be responsible for any memory management and could have a 
> shared pointer version as well.
>
> For example:
> template<typename T>
> class protected_ptr
> {
>     T * ptr;
>
>     // ...
>     T * get();
>     const T * get() const;
>
>     // ...  including operator* and operator->
> }
>
> class Foo
> {
>     protected_ptr<Bar> _bar;
>
>     void Func1()
>     {
>         _bar->NonConstFunc();
>         _bar->ConstFunc();
>     }
>
>     void Func2() const
>     {
>         _bar->NonConstFunc();  // Compile error
>         _bar->ConstFunc();     // Ok
>     }
> }
>
> Ray Logel
>
>
The could be useful to propagate constness, however it looks like the 
boost smart pointers deliberately dont do that.
The following is an excerpt from shared_ptr's faq 
(http://www.boost.org/doc/libs/1_38_0/libs/smart_ptr/shared_ptr.htm#functions):

"A. Shallow copy pointers, including raw pointers, typically don't 
propagate constness. It makes little sense for them to do so, as you can 
always obtain a non-const pointer from a const one and then proceed to 
modify the object through it.shared_ptr is "as close to raw pointers as 
possible but no closer"."

BR, Dmitry