Github user StephanEwen commented on the pull request:

    https://github.com/apache/incubator-flink/pull/203#issuecomment-64698910
  
    I like the direction of this pull request. Here are some thought what we 
could improve:
    
      - Keeping the UnknownTypeInfo all the way and actually trying to work 
with it will shadow problems. At much later points, when someone tries to use a 
POJO field on the type info, an error will occur, at a point that is 
disconnected from the source of the problem.
    
      - How about we rename the `UnknownTypeInfo` to `MissingTypeInfo` and use 
it only as a place-holder for the `returns()` hint method, which exchanges that 
type info by the proper one.
    
      - We could make sure that type extraction failures are recognized early, 
by having the `getType()` method on the DataSet throw an error if only a 
`MissingTypeInfo` exists.
    
      - Getting Generic Lambdas to run with this may not be a good idea. This 
goes against my original suggestion to keep this for the purpose of local 
development with OracleJDK, but in hind-sight, I think things will get quite 
intransparent to reason about and hard to maintain/debug/fix.



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