[SOLVED] VectorData merge function question

Hey,

I was looking for copying VectorData and i found the merge function.
Here is the source code of merge function :

/// merging several Data from a VectorData into a large Data (of the same type)
    static void merge(Data<T>& outputData, const vectorData<T>& vectorData)
    {
        size_t nbInput = vectorData.size();
        size_t nbElems = 0;

        for( size_t i=0 ; i<nbInput ; ++i )
            nbElems += vectorData[i]->getValue().size();

        helper::WriteOnlyAccessor< Data<T> > out = outputData;
        out.clear();
        out.reserve(nbElems);
        for( size_t i=0 ; i<nbInput ; ++i )
        {
            helper::ReadAccessor< Data<T> > in = vectorData[i];
            for( size_t j=0, jend=in.size() ; j<jend ; ++j )
                out.push_back(in[j]);
        }
    }

But I encounter than Data was the “output” and it feels weird from me …
The code of merge function, use push_back data in data, which looks like Data is a VectorData.

Finally here is my question, why Data has the same behavior of VectorData (push_back) ? What is the real difference between Data and VectorData, if Data can be considered as a vector ?