[zeromq-dev] (no subject)

[Ilja Golshtein]

Martin, All,

you are right, there is no 100% similarity with std::string.

Trying to look at the message_t from the same angle we should conclude:
1. close() in not const regardless BLOB - it destroys message object. And there is no such a method by the way. Did you ever see const destructor?
2. copy() is not a const method because it changes the object. Though argument of the method should be const message_t *msg_. Initially I was confused by copy semantic. If argument were marked as constant I would not!
3. move() is not a const method and it's argument is not const*
4. size() is undoubtedly const
5. good idea to have const and non const data() methods. Absence of overloading at C level could be simply ignored.
6. const_message_t  is logical from C++ standpoint, though I think it worth introducing if any performance gain is possible.

Thanks.

22.04.2011, 00:49, "Martin Sustrik" <sustrik at 250bpm.com>:
> Ilja, Andrew,
>
> std::string is able to make the reference counting trasparent to the
> user using CoW semantics. Unfortunately, with zmq_msg_t we don't have
> this option.
>
> The place where the abstraction leaks most is zmq_msg_close() function.
> It removes one reference from the BLOB (const operation) and if it
> reaches zero, it deletes the BLOB (non-const operation).
>
> The most sensible option seems to be to treat close as non-const
> operation. The ugly part is the asymmetricity between zmq_msg_copy()
> which adds a reference and zmq_msg_close() which removes a reference.
> Former is const operation while later is non-const operation.
>
> Another problem is getting a const data pointer from const message
> object. C doesn't support polymorphism so something like this is not
> possible:
>
>      void *zmq_msg_data (zmq_msg_t *msg);
>      const void *zmq_msg_data (const zmq_msg_t *msg);
>
> Thoughts?
> Martin
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-- 
Best regards,
Ilja Golshtein.