You are correct that all of these casts can be done. We omitted them
explicitly because of what you said that we did not want to loose
precision. We should be able to downcast when users ask explicitly
for it, but we don't want to do this implicitly.
Alan.
On Mar 24, 2010, at 2:47 PM, Anil Chawla wrote:
Hi,
I know that Pig has logic for casting inputs to the expected data
types
when invoking a UDF and I understand that this logic resides in the
TypeCheckingVisitor class. I am curious to know why certain casts
have been
omitted from the "castLookup" map. Specifically, I do not see any
entries
for casting a more precise numeric type (e.g. Double) to a less
precise
numeric type (e.g. Integer). Any reason why all down conversions of
numeric
types have been omitted? Is it because we do not want to perform any
automatic casts that lead to a loss of precision (loss of data)?
In my situation, we are trying to abstract all numeric data types
into a
single "number" type. If a UDF takes a numeric parameter, we want
Pig to
invoke that UDF with any numeric argument, regardless of whether the
argument must be upconverted or downconverted. We are OK with the
loss of
precision in that circumstance. As a result, we added the following
to the
"castLookup" map:
castLookup.put(DataType.LONG, DataType.INTEGER);
castLookup.put(DataType.FLOAT, DataType.LONG);
castLookup.put(DataType.FLOAT, DataType.INTEGER);
castLookup.put(DataType.DOUBLE, DataType.FLOAT);
castLookup.put(DataType.DOUBLE, DataType.LONG);
castLookup.put(DataType.DOUBLE, DataType.INTEGER);
All of these casts seem to work fine our tests. Other than loss of
precision, is there any reason why adding these casts might be a bad
idea?
Thanks,
-Anil
