[Development] Proposal for an efficient and robust (de)serialization mechanism working with Qt-supported data

[Terry Williams]

Please remove me from your mailing list

Thanks.

On Tue, Aug 27, 2019 at 5:46 AM Arnaud Clere <arnaud.clere at minmaxmedical.com>
wrote:

> Hi all,
>
>
>
> Qt handles a broad spectrum of data both in and out of RAM and Qt users
> routinely need to read/write such data from/to their domain-specific C++
> types.
>
> But doing so can feel much more complicated than it should be: e.g.
> unexpected QVariant conversions, unknown QDataStream versions, complex
> QAbstractItemModel requirements, specific QCborStreamReader protocol, ...
>
> Moreover, writing such boilerplate code is time-consuming, error-prone,
> and boring.
>
>
>
> JSON demonstrates that having a simple data model can simplify exchanging
> data between software components. But it cannot meet all the technical
> requirements that data must meet here and there.
>
>
>
> I am proposing to add to Qt a simple-to-use (de)serialization mechanism
> that can achieve better write performance and read robustness than current
> alternatives.
>
> It does not define a new generic data type: QVariant/List/Map,
> Q*ItemModel, QJsonValue, ... are here to meet various sets of requirements.
>
> It just defines a generic, efficient and robust templated function to
> ‘bind’ such data with any C++ type:
>
>                QBind<T> ::bind(Value&& v, T& t)
>
>
>
> It is not unit-tested but a sample and benchmark shows it can be made to
> work efficiently with:
>
> - Qt containers (read/write)
>
> - QMetaObject (read/write)
>
> - QVariant* (read/write)
>
> - QJsonValue (read/write) + ad-hoc JSON reader/writer
>
> - QCborValue (read/write), QCborStreamReader + ad-hoc CBOR writer
>
> - QSettings (read/write)
>
> - QXmlStreamWriter
>
> - QAbstractItemModel (write)
>
> - QDataStream (write)
>
>
>
> The simplest way to enable it for a C++ type is to use QMetaObject when
> available through a macro (QBIND_*_WITH_METAOBJECT).
>
> Best performance can only be attained by defining simple bind(Value&& v)
> methods that usually work for both read and write:
>
>
> https://gricad-gitlab.univ-grenoble-alpes.fr/modmed/modmedLog/blob/master/tests/QBind/README.md#extending-qbind-to-c-types
>
>
>
> Finally, since a single QBind<T> function cannot fulfill all the needs,
> its fluent interface allows writing custom binds akin to Python list
> comprehensions…
>
>
>
> I would be happy to hear if you feel like this would be a useful
> contribution to Qt, or to answer your technical questions and arguments.
>
>
>
> Arnaud
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>
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