Performance in functions with QList

[john_god]

Is there a significant performance issues between the next 2 functions ?

void cos(QList<Complexo> &x, QList<Complexo> &y)
{
    y.clear();
 
    for(int i=0;i < x.size(); i++)
    {
        y.append(cos(x[i]));
    }
}
 
QList<Complexo> cos(QList<Complexo> & x)
{
    QList<Complexo> y;
 
    for(int i=0;i < x.size(); i++)
    {
        y.append(cos(x[i]));
    }
 
    return y;
}

void cos(QList<Complexo> &x, QList<Complexo> &y)
{
    y.clear();

    for(int i=0;i < x.size(); i++)
    {
        y.append(cos(x[i]));
    }
}

QList<Complexo> cos(QList<Complexo> & x)
{
    QList<Complexo> y;

    for(int i=0;i < x.size(); i++)
    {
        y.append(cos(x[i]));
    }

    return y;
}

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The second seems more elegant but returning a large QList, will be slower ?

[Lykurg]

Go for the second variant. It is fast since QList is one of Qt's implicit data sharing class (In the docs under: Implicit Sharing). So only a pointer will be passed back and that is very fast

[tbscope]

If you're interested, here's some insight into QList:
http://marcmutz.wordpress.com/2010/0...dered-harmful/

[john_god]

Thanks Lykurg and tbscope. Second variant shall be .
I checked MarcMutz link "QList considered harmful", didn´t know that. However there's some contradictions with Qt Nokia docs. Always thought QList was preferable to QVector. I have no experience with STL containers, never used them. So I'am sticking with QList, I like it's sintaxe better, and it suits my case.