Re: [boost] Why no non-null smart pointers?

Subject: Re: [boost] Why no non-null smart pointers?
From: Rob Stewart (robertstewart_at_[hidden])
Date: 2014-04-29 05:22:27

On April 28, 2014 11:20:35 AM EDT, Jeff Hill <johill_at_[hidden]> wrote:
>Ross MacGregor wrote
>> "Johan RÃ¥de" 
>> 
>> I know it is an insane idea to suggest changing the entire 
>> boost::smart_ptr library to a boost::smart_ref library, but I 
>> think it may actually be the right thing to do. Does anyone 
>> agree?
>
>I also find the nill state of shared_ptr to be a liability when
>designing
>interfaces.  The primary purpose of shared_ptr when used in an
>interface
>context is to convey ownership, and almost always it feels wrong to
>also
>provide simultaneously an option to convey ownership of nothing. The
>poor
>user is left with the responsibility of testing every shared_ptr he has
>received for null state before using it, but its easy to forget and the
>compiler provides no assistance. 

You've overlooked the use case of reclaiming ownership from smart_ptr. There's nothing left for it to own after that. (You can't replace it with a default constructed instance, as there may be no default constructor. Any other value you choose would be a sentinel value and you'd want to detect that in many contexts, so checking for null is more straightforward.)

OTOH, you could justify a new class that has no reset() and that rejects null pointers, so it is never null, yet has shared ownership semantics.

___
Rob

(Sent from my portable computation engine)