Hi Jeyhun,
I understand your argument about "Rich" in RichFunctions. Perhaps I'm
just being too puritan here, but let me ask this anyway:
What is it that makes something a function? To me a function is
something that takes zero or more arguments and possibly returns a value
and while it may have side-effects (as opposed to "pure functions" which
can't), it doesn't have any life-cycle of its own. This is what, in my
mind, distinguishes the concept of a "function" from that of more
vaguely defined concepts.
So if we add a life-cycle to a function, in that understanding, it
doesn't become a rich function but instead stops being a function
altogether.
You could say it's "just semantics" but to me precise use of language in
the given context is an important foundation for good engineering. And
in the context of programming "function" has a precise meaning. Of
course we can say that in the context of Kafka Streams "function" has a
different, looser meaning but I'd argue that won't do anyone any good.
On the other hand other frameworks such as Flink use this terminology,
so it could be that consistency is the reason. I'm guessing that's why
the name was proposed in the first place. My point is simply that it's a
poor choice of wording and Kafka Streams don't have to follow that to
the letter.
Cheers,
Michal
On 23/05/17 13:26, Jeyhun Karimov wrote:
Hi Michal,
Thanks for your comments.
To me at least it feels strange that something is called a
function yet doesn't follow the functional interface definition of
having just one abstract method. I suppose init and close could be
made default methods with empty bodies once Java 7 support is
dropped to mitigate that concern. Still, I feel some resistance to
consider something that requires initialisation and closing (which
implies holding state) as being a function. Sounds more like the
Processor/Transformer kind of thing semantically, rather than a
function.
- If we called the interface name only Function your assumptions
will hold. However, the keyword Rich by definition implies that we
have a function (as you described, with one abstract method and etc)
but it is rich. So, there are multiple methods in it.
Ideally it should be:
public interface RichFunction extends Function { // this is the
Function that you described
void close();
void init(Some params);
...
}
The KIP says there are multiple use-cases for this but doesn't
enumerate any - I think some examples would be useful, otherwise
that section sounds a little bit vague.
I thought it is obvious by definition but I will update it. Thanks.
IMHO, it's the access to the RecordContext is where the added
value lies but maybe I'm just lacking in imagination, so I'm
asking all this to better understand the rationale for init() and
close().
Maybe I should add some examples. Thanks.
Cheers,
Jeyhun
On Mon, May 22, 2017 at 11:02 AM, Michal Borowiecki
<michal.borowie...@openbet.com <mailto:michal.borowie...@openbet.com>>
wrote:
Hi Jeyhun,
I'd like to understand better the premise of RichFunctions and why
|init(Some params)|,|close() |are said to be needed.
To me at least it feels strange that something is called a
function yet doesn't follow the functional interface definition of
having just one abstract method. I suppose init and close could be
made default methods with empty bodies once Java 7 support is
dropped to mitigate that concern. Still, I feel some resistance to
consider something that requires initialisation and closing (which
implies holding state) as being a function. Sounds more like the
Processor/Transformer kind of thing semantically, rather than a
function.
The KIP says there are multiple use-cases for this but doesn't
enumerate any - I think some examples would be useful, otherwise
that section sounds a little bit vague.
IMHO, it's the access to the RecordContext is where the added
value lies but maybe I'm just lacking in imagination, so I'm
asking all this to better understand the rationale for init() and
close().
Thanks,
Michał
On 20/05/17 17:05, Jeyhun Karimov wrote:
Dear community,
As we discussed in KIP-149 [DISCUSS] thread [1], I would like to initiate
KIP for rich functions (interfaces) [2].
I would like to get your comments.
[1]
http://search-hadoop.com/m/Kafka/uyzND1PMjdk2CslH12?subj=Re+DISCUSS+KIP+149+Enabling+key+access+in+ValueTransformer+ValueMapper+and+ValueJoiner
<http://search-hadoop.com/m/Kafka/uyzND1PMjdk2CslH12?subj=Re+DISCUSS+KIP+149+Enabling+key+access+in+ValueTransformer+ValueMapper+and+ValueJoiner>
[2]
https://cwiki.apache.org/confluence/display/KAFKA/KIP-159%3A+Introducing+Rich+functions+to+Streams
<https://cwiki.apache.org/confluence/display/KAFKA/KIP-159%3A+Introducing+Rich+functions+to+Streams>
Cheers,
Jeyhun
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