[jira] [Created] (FLINK-7194) Add getResultType and getAccumulatorType to AggregateFunction

["Fabian Hueske (JIRA)" <ji...@apache.org>]

Fabian Hueske created FLINK-7194:
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             Summary: Add getResultType and getAccumulatorType to AggregateFunction
                 Key: FLINK-7194
                 URL: https://issues.apache.org/jira/browse/FLINK-7194
             Project: Flink
          Issue Type: Improvement
          Components: Table API & SQL
    Affects Versions: 1.4.0
            Reporter: Fabian Hueske


FLINK-6725 and FLINK-6457 proposed to remove methods with default implementations such as {{getResultType()}}, {{toString()}}, or {{requiresOver()}} from the base classes of user-defined methods (UDF, UDTF, UDAGG) and instead offer them as contract methods which are dynamically 

In PR [#3993|https://github.com/apache/flink/pull/3993] I argued that these methods have a fixed signature (in contrast to the {{eval()}}, {{accumulate()}} and {{retract()}} methods) and should be kept in the classes. For users that don't need these methods, this doesn't make a difference because the methods are not abstract and have a default implementation. For users that need to override the methods it makes a difference, because they get IDE and compiler support when overriding them and the cannot get the signature wrong.

Consequently, I propose to add {{getResultType()}} and {{getAccumulatorType()}} as methods with default implementation to {{AggregateFunction}}. This will make the interface of {{AggregateFunction}} more consistent with {{ScalarFunction}} and {{TableFunction}}.

What do you think [~shaoxuan], [~RuidongLi] and [~jark]?



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