Optimize deserialization

[coryan]

As @fornwall notes:

The generated deserializers track duplicate fields with a HashSet, which hashes each insertion and allocates storage as fields are recorded.

This could be avoided with a bitset: each field could get a known index between 0 and N, and N is known at compile time.

I am opening this issue so we can discuss ideas, tradeoffs, and quantify the wins.

[coryan]

@fornwall Sounds like a plausible improvement. Do you have any measurement showing how much better this is? Maybe for a typical response? Or for an atypical (large) response?

Something that says: compared to the overall time to deserialize the response this is a X% improvement. Include details of the compiler, CPU, and OS if available.

[coryan]

Thoughts?