Ruidong Li commented on FLINK-7194:

[~fhueske]I agree to your suggestion, but the {{getResultType()}} in 
{{ScalarFunction}} is different from  {{TableFunction}} and 
{{AggregateFunction}}, what about if we put a ban on overloading {{eval()}} in 
{{ScalarFunction}}? That will result in better consistence.

> 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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