Re: [Interest] QJsonDocument::fromVariant failing with list

[Jason H]

One hack I would workfor me is a new class, QVariantMapList, (List of QVariantMaps) which is really all I need at the moment, unless there'd be a need for QVariantListList too? (That's a terrible name though)

 

Ultimately, I just want to express JSON as closely as I can in C++.

Ideally:

	QVariantMap map {
		{"err", QVariant()},
		{"letters", QVariantMapList {
				{{"a",1}},
				{{"b",2}},
				{{"c",3}}
		}}
	};

 

Sent: Wednesday, June 09, 2021 at 10:15 AM

From: "Jérôme Godbout" <godbo...@amotus.ca>

To: "Thiago Macieira" <thiago.macie...@intel.com>, "interest@qt-project.org" <interest@qt-project.org>

Subject: Re: [Interest] QJsonDocument::fromVariant failing with list




I understand the homogenous part when you do decoding, but encoding to json should support the homogenous, isn’t? why not? I understand that the decode of that json would alter the type.

 

QList<QVariantMap>  encode json  [{‘a’: ‘b’}, {‘c’:’d’}]   decode json   QList<QVariant> 

 

Should be possible as long as QList<T> where T can be convert to QVariant. Maybe an external converter function should be used. If this is not supported, is there a way where we could trap this at compile time warning?

 

Maybe there is a limitation I do not see here.

 

 


From: Interest <interest-boun...@qt-project.org> on behalf of Thiago Macieira <thiago.macie...@intel.com>

Date: Wednesday, June 9, 2021 at 10:08 AM

To: interest@qt-project.org <interest@qt-project.org>

Subject: Re: [Interest] QJsonDocument::fromVariant failing with list



On Wednesday, 9 June 2021 00:34:40 PDT Allan Sandfeld Jensen wrote:

> > QList is not a type, it's a template. Neither QVariant nor QJsonDocument

> > can know all possible QList instantiations. So they have coded only a few

> > (QVariantList and QStringList only, possibly QVector<QVariant> and

> > QVector<QString> in Qt 5 too, I don't remember).

>

> I guess our system could detect QList<QVariant> as QVariantList and

> QList<QString> as QStringList. They should be binary identical anyway.



They already do.



The problem is QList of other things that it's not coded for, like

QList<QVariantMap> in this case, or QList<int> or QList<bool>. Since JSON

arrays are not expected to be homogeneous, QJsonDocument does not support

them.



--

Thiago Macieira - thiago.macieira (AT) intel.com

  Software Architect - Intel DPG Cloud Engineering







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