Hot to convert (cast) QHash<int, StructOfQByteArray1AndQbyteArray2> to QHash<int, QByteArray1> with minimum resource cost?

Kofr

ok. let's find out how well do you know C++.
ok we have

struct StructOfQByteArray1AndQbyteArray2 {
    QByteArray array1;
    QByteArray array2;
}

Hot to convert (cast) QHash<int, StructOfQByteArray1AndQbyteArray2> to QHash<int, QByteArray1> with minimum resource cost?

where I want to use this?
when working with QAbstractItemModel I implement method QHash<int, QByteArray> QAbstractItemModel::roleNames() const but in app I have more complex QHash<int, StructOfQByteArray1AndQbyteArray2> with some extra data.

mrjj

well if u want to avoid copy bytearray
maybe use something like
QHash<int, QByteArray1 *>
and set to point to the real QByteArray1; ?

Kofr

@mrjj but I have to return exactly data, not pointer QHash<int, QByteArray> QAbstractItemModel::roleNames() const

mrjj

@Kofr said:

ahh its something you must return.

Well i think u need copy then since i doubt there is way to cast the original
StructOfQByteArray1AndQbyteArray2

SGaist

Hi,

From a C++ POV: you can't do such a cast.

What resources do you want to optimize ? Speed ? Memory use ?

Kofr

@SGaist Speed. So you want to say that it is ok to manually fill in QHash<int, QByteArray> before returning and just allow data to be copied as rvalue?

SGaist

I'm just saying that you can't cast (as in static_cast, dynamic_cast etc.) such a hash of int and struct to a hash of int and QByteArray.

Are your role names going to be dynamically created ? Changed ?

Kofr

@SGaist yes, I will have custom roles for some delegates.

SGaist

Ok but these roles are already known, no ?