Nested QVariantMap

Question

I'm using nested QVariantMap and have a problem with defining a method that takes a path (string list) and returns the pointer to low-level QVariantMaps:

QVariantMap * getQVariantMap( QStringList spec) const {
    QVariantMap * deep_p = this->hash_p;

    for( QStringList::const_iterator it = spec.begin();
                                     it!= spec.end();
                                   ++it)
    {
        QVariantMap::const_iterator i = hash_p->find( *it);
        if( i == hash_p->end())
            return 0x00;

        res_p = & i.value().toMap();
    }

    return res_p;
}

...

QVariantMap map, level1, level2;
level2["L2"] = "bazzinga!";

level1["L1"] = QVariant::fromValue( level2);
level1["foo"] = "foo";

map["L0"] = QVariant::fromValue( level1);
map["foo"] = "foo";

QStringList qsl;
            qsl.append( "L1");
            qsl.append( "L0");

QVariantMap * qvm = getQVariantMap( qsl);//pointer to level2 part of the nested QVariantMap.

qvm[ "foo"] = "baz";

//map[ "L0"].toMap()[ "L1"].toMap()[ "foo"] == "baz";

...

I got the following error:

taking address of temporary [-fpermissive]

and I know why. The problem is that I need to get the pointer to the part of the nested structure, but I can't get reference to the internals of the QVariant. I tried to use data_ptr, suggested in post Assigning to nested QVariantMap, with no luck. For the obvious reasons I don't want to make special wrappers on insert/remove/value (that why, as I understood, accepted answer in linked topic is not my case).

I tried:

to store QPointer inside QVariant -- with no luck because QVariant is not QObject;
to store pointer using QVariant::fromValue( QVariantMap *), but when I making toMap() call it return the QVariantMap, and not the pointer, so I got the taking-address-of-temporary-error again. And either way, I don't think that this is what I want.

How someone should do it properly?

Why do you store your QVariantMap as a pointer? Why not like a value? — vahancho, Jul 10 '14 at 15:47
I store it as a QVariant, that I got using QVariant::fromValue( QVariantMap). — Valentin T., Jul 10 '14 at 15:49
Well, than I would write it like `res_p = new QVariantMap(i.value().toMap());` — vahancho, Jul 10 '14 at 15:50
You should not use `new` on QVariant and QVariantMap or use `QVariant*` type. They should be passed by value. — Pavel Strakhov, Jul 10 '14 at 21:33
@vahancho, I thought I would get a pointer to the map clone, using `new`, am I wrong? — Valentin T., Jul 11 '14 at 09:51
@ValentinT., you get the pointer to the temporary **copy** of map - that is where the error comes from. You need to create a new object with `new` using the copy constructor. — vahancho, Jul 11 '14 at 09:57
But in this case If I'll modify it, it will not propagate changes. — Valentin T., Jul 11 '14 at 10:03

Nested QVariantMap

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