Suggestion: use basic_staj_event::length_ for arrays/objects of known size

[ecorm]

I'm using the cursor interface to decode JSON, MsgPack, CBOR, etc into my own variant type (similar to your basic_json). For the staj_event_type::begin_array and staj_event_type::begin_object events, it would be useful if basic_staj_event::length_ contained the number of elements when this is known (e.g. MsgPack and CBOR definite arrays/maps). This would allow me to reserve the data structures that will contain the elements, thus avoiding reallocations. A length_ of zero could be a special value that means "unknown length".

[danielaparker]

That's a good suggestion, it was easy to implement, and is currently on master.

I've added a size() accessor function to basic_staj_event. If the event type is a key or a string_value or a byte_string_value,
it returns the size of the key or string or byte string value. If the event type is a begin_object or a begin_array, it returns the size of the object or array if known, otherwise 0. For all other event types, it returns 0.