Implementation of QVector

[ChristianHeusel]

According to the documentation over at https://doc.qt.io/qt-5/qvector.html#at there is only one implementation for QVector::at(), of which applies constness.
I just assumed from my STL expierience that there would be one which is non-const.
version of the function what would make sense in my opinion.
I got the error with the following codesnippet, please explain if i get something entirely wrong :)

void MyClass::on_MyComboBox_currentTextChanged(const QString& newtext) {
   auto index = _ui->MyComboBox->currentIndex();
   _myQVector.at(index) = arg1;
   for(const auto& element : _myQVector) qInfo() << element;
}

[dheerendra]

You can't assign like this. at returns a value and not variable

[mrjj]

Hi
Oddly enough, there is no non const version of at()
However, the operator [] has one
https://doc.qt.io/qt-5/qvector.html#operator-5b-5d

[ChristianHeusel]

@dheerendra

@dheerendra said in Implementation of QVector:

[..] at returns a value and not variable

Yeah but why is that the case? As far as i know there could be a non-const version like this:

T& QVector::at()

For the operator[] there is a non-const and a const one, why is this not the case with at()?!

[aha_1980]

@ChristianHeusel the soley reason at() exists is to provide a read-only access to make sure the implicitely shared container does not detach.

For write access, use []

regards

[ChristianHeusel]

@aha_1980 Supposing that your answer is correct my question is now invalid since the purpose of std::vector::at() is then a diffrent one than it is in QT.
Question will be marked as resolved :)

[aha_1980]

@ChristianHeusel it's indirectly stated here: https://doc.qt.io/qt-5/qvector.html#operator-5b-5d (a bit hidden)

"non-const operators can cause a deep copy".