Default constructor of UDF gets called for UDF with parameterised constructor , 
if the udf has a getArgToFuncMapping function defined

                 Key: PIG-969
             Project: Pig
          Issue Type: Bug
          Components: impl
            Reporter: Thejas M Nair

This issue is discussed in . I am 
able to reproduce the issue. While it is easy to fix the udf, it can take a lot 
of time to figure out the problem (until they find this email conversation!).

The root cause is that when getArgToFuncMapping is defined in the udf , the 
FuncSpec returned by the method replaces one set by define statement . The 
constructor arguments get lost.  We can handle this in following ways -

1. Preserve the constructor arguments, and use it with the class name of the 
matching FuncSpec from getArgToFuncMapping . 
2. Give an error if constructor paramerters are given for a udf which has 
FuncSpecs returned from getArgToFuncMapping .

The problem with  approach 1 is that we are letting the user define the 
FuncSpec , so user could have defined a FuncSpec with constructor (though they 
don't have a valid reason to do so.). It is also possible the the constructor 
of the different class that matched might not support same constructor 
parameters. The use of this function outside builtin udfs are also probably not 

With option 2, we are telling the user that this is not a supported use case, 
and user can easily change the udf to fix the issue, or use the udf which would 
have matched given parameters (which unlikely to have the getArgToFuncMapping 
method defined).

I am proposing that we go with option 2 . 

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