qml can not recognize the c++ parameters with &

[anda_skoa]

It is likely that the fileUrls property of FileDialog is actually of type QStringList, so passing the value to the C++ function might not involve any conversions.

In which case passing by const reference would not create a copy. Even passing by value would be cheap since QList is implicitly shared (reference counted) so copying is a relatively cheap operation.

Do you have any benchmark that shows the operation to be slow?

Cheers,
_

[stereoMatching]

It is likely that the fileUrls property of FileDialog is actually of type QStringList

I hope so, but it is QList<QUrl> but not QList<QString>
in the document of the FileDialog, there are nothing called fileUrl but filePath
and the qml type of filePath is list<string>
maybe this is because I am using 5.1RC, so the incoherent of the codes and the document still exist

Even passing by value would be cheap since QList is implicitly shared (reference counted)

Hard to said, because I need to modify the content of QList(sorting)

Do you have any benchmark that shows the operation to be slow?

No, it is not a bottleneck yet(maybe in the future, it is)
but the experience from c++(and c) make me feel nervous
when I have to copy the data which could be "moved" or take the reference usually

[anda_skoa]

I hope so, but it is QList<QUrl> but not QList<QString>

I see, should still be ok. Your slot has the same type for its arguments.

Hard to said, because I need to modify the content of QList(sorting)

Depends on the reference count at the time of modification. If the slot is the only one holding the list at that time it won't need to copy.
If there is another owner, then there will be a copy of the list. Since you don't change the url data the QUrl instances should still be the same.

No, it is not a bottleneck yet(maybe in the future, it is)
but the experience from c++(and c) make me feel nervous
when I have to copy the data which could be "moved" or take the reference usually

Due to the implicit sharing, copying is a lot like moving, actual copying happening on modification (copy on write).

Cheers,
_

[wysota]

Depends on the reference count at the time of modification. If the slot is the only one holding the list at that time it won't need to copy.

The reference count will not be 1 as the caller has a handle on the list as well.

[stereoMatching]

I see, should still be ok. Your slot has the same type for its arguments.

Because I want to make my question become easier to understand, I change the type of the example
the real type are a little bit tricky, one is "QUrl" and another one is "QString"
hope this could be fix in the release version