Strange stream object copying while parsing

[miloyip]

https://code.google.com/p/rapidjson/issues/detail?id=78

In a rapidjson reader class there's some strange code:

template<typename Stream>
void SkipWhitespace(Stream& stream)
{
    Stream s = stream;  // Use a local copy for optimization
    while (s.Peek() == ' ' || s.Peek() == '\n' || s.Peek() == '\r' || s.Peek() == '\t')
        s.Take();
    stream = s;
}

Why stream object is reassigned two times, what optimization this gives comparing to direct accessing it via reference? What if stream object copying is a heavy process by itself and also can cause an exception? What if I want to create stream class with non-copyable semantic? For me all of this is a clear pessimization instead of optimization.

[miloyip]

I have re-tested the impact after removal of these "optimizations". Results.
There is around 10%-20% overheads if disabling this "overhead".
I will try to add a switch which is specified by stream class.