Remove some redundancy from the DValue hierarchy: all subclasses had a 'type' field and identical implementations of virtual function getType(). Move these to DValue itself, and make getType() non-virtual.

char[] get()
{
    return "hello";
}

void param(char[] s)
{
}

void refparam(ref char[] s)
{
}

void main()
{
    char[] dstr = get();
    param(dstr);
    refparam(dstr);
}