Can't assign begin() to const_iterator?

[Stephen Chu]

The following code is getting me "Conversion from 'Json::ValueIterator' to non-scalar type 'Json::ValueConstIterator' requested" error with gcc 4/2:

Json::Value a;
Json::Value::const_iterator n=a.begin();

Any idea why? There is a

const_iterator begin() const;

defined. Wonder why it's not used?