[Development] ODP: RFC: Deprecating setSharable / isSharable in our containers and QString

[Nowacki Jedrzej]

I agree that the code is fragile and it is not the best api ever, that is why I believe we could deprecate it. 

I remember the idea of injecting allocator into containers, I do not remember why it died (was it memory expensive?). From api perspective it would be a better solution.

Cheers,
  Jędrek
________________________________________
Od: development-bounces+jedrzej.nowacki=digia.com at qt-project.org [development-bounces+jedrzej.nowacki=digia.com at qt-project.org] w imieniu Thiago Macieira [thiago.macieira at intel.com]
Wysłano: 20 lutego 2014 18:01
Do: development at qt-project.org
Temat: Re: [Development] ODP: RFC: Deprecating setSharable / isSharable in      our     containers and QString

Em qui 20 fev 2014, às 12:14:24, Nowacki Jedrzej escreveu:
> H,
>
>   One hand raised.
>
>   The original use case is buried in the Qt history, when I was asking /
> digging why we had that, I found that in some really rare and obscure cases
> it may be useful. For example when you want to control the life time of a
> data in your container. Imagine QVector::fromRawData which doesn't copy the
> data but just update d, the internal header:
>
> char t* = strdup(...);
> {
>   QVector<char> tmp = QVector<char>::fromRawData(t);
>   tmp.setSharable(false);
>   Qt.Api.call(tmp);
> }
> free(t);
>
>   In my opinion we can safely deprecate it.

The problem with that is that it might cause extra memory allocations when
something accidentally copies it in your called function. And you also wrote a
nice example that calls a function, instead of trying to return it (which
would trigger a deep copy).

In any case, you may remember from the pre-5.0 discussion that I want to
introduce an "external data" type of handler. So the above would be:

        char *t = strdup(...);
        QVector<char> tmp = QVector<char>::fromRawData(t, strlen(t), free);
        Qt.Api.call(tmp);

When all copies go out of scope, QVector calls free(data()).

--
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center

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