RE: [boost] Re: Interest in smart pointer with value semantics?

From: Reece Dunn (msclrhd_at_[hidden])
Date: 2004-01-04 07:57:06

Dan W. wrote:

>>class X
>>{
>>     smart_ptr<My_polymorhic_type> p_;
>>public:
>>     int bar() const
>>    {
>>        return p_->this_is_also_a_const_function(); // compile time error 
>>if
>>not
>>     }
>>};

>That's neither a const, nor a non-const function of p_, you're calling;  
>it's a function of what p points to. That a function is const means that it 
>doesn't change the class state, i.e.: what _address_ the pointer points to. 
>But the target at that address is _not_ part of the state of this class, so 
>why should the constness of a member function of _this_ class have to bear 
>responsibility for some class elsewhere, just because we have its pointer?

The problem in this case is that the function bar() is const, and thus so 
must the this pointer to the class. I think this is what is causing the 
problem in this example.

But, let me point out that this works to retain the const-ness of the 
program: declaring bar() to be const is saying that you intend the function 
to be a *read* method (as it is returning an int).

If you intend to violate this, you need to add a const_cast around the 
pointer call, making it explicit that this is what you want to do, but then 
why is bar() const?

Regards,
Reece

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