flink-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Stephan Ewen <se...@apache.org>
Subject Re: Issues with Java 8 Lambda Expressions
Date Sun, 02 Nov 2014 15:22:39 GMT
An alternative would be to go for

env.fromElements(1, 2, 3)
.flatMap((Integer i, Collector<Integer> o) -> o.collect(i) ,
returns("Integer"))
.print();

"returns" would here be a static method that creates the type info.

That would require to add an additional parameter, but allow us to keep the
immediate checks. Deferring the checks will make things harder to
understand for users as well...
Am 30.10.2014 11:44 schrieb "Stephan Ewen" <sewen@apache.org>:

I think that would look nice.

How easy is that to implement? With that change, we could not initialize
the type info in the constructor any more, but would have to change
everything to lazy initialization, which makes it complicated and error
prone...

On Wed, Oct 29, 2014 at 4:26 PM, Timo Walther <flink@twalthr.com> wrote:

> What do you think about something like:
>
> env.fromElements(1, 2, 3)
> .flatMap((Integer i, Collector<Integer> o) -> o.collect(i)).returns("
> Integer")
> .print();
>
> This looks to me like the most readable and user-friendly solution. We
> only need to change the internals of DataSet a little bit, such that a
> possible TypeExtractor Exception is stored temporarily and thrown by the
> operator that follows if "returns()" was not called.
>
> Regards,
> Timo
>
>
>
> On 28.10.2014 15:34, Stephan Ewen wrote:
>
>> Is it possible to use a static method "hint" to create the hinting wrapper
>> function?
>>
>> Something like
>>
>> DataSet.map(hint( (x) -> x.toString() , String.class));
>>
>> If we go for option (1), I would suggest to call the methods just "from"
>> and overload them for String, Class, and TypeInformation
>>
>>
>> Stephan
>>
>>
>> On Tue, Oct 28, 2014 at 3:27 PM, Timo Walther <flink@twalthr.com> wrote:
>>
>>  Hi all,
>>>
>>> currently the Eclipse JDT compiler was the only compiler that included
>>> generic signatures for Lambda Expressions in class files which is
>>> necessary
>>> to use them type-safe in Flink. Unfortunalely, this "feature" was
>>> considered as a "bug" and had been thrown out with Eclipse 4.4.1. This is
>>> why Lambdas do not work properly with the current version of Eclipse. I
>>> have opened a bug for that (see https://bugs.eclipse.org/bugs/
>>> show_bug.cgi?id=449063).
>>>
>>> The question is: Independent of the decision of the Eclipse JDT team, how
>>> do we want to deal with missing return type information?
>>>
>>> Option 1)
>>> Add a separate TypeInformation argument to each Java API operator. Leads
>>> to blown up API...
>>> .map((x)->x + 1, TypeInformation.fromString("Integer"))
>>> .flatMap((in, out)->out.collect(in), TypeInformation.fromClass(
>>> Integer.class))
>>>
>>> Option 2)
>>> Introduce a wrapper class which implements ResultTypeQueryable. Leads to
>>> complicated syntax...
>>> .map(TypeHint.map((x)->x + 1, "Integer"));
>>> .map(TypeHint.map((x)->x + 1, Integer.class));
>>>
>>> What are your opinions? Or any other ideas?
>>>
>>>
>>> Regards,
>>> Timo
>>>
>>>
>

Mime
  • Unnamed multipart/alternative (inline, None, 0 bytes)
View raw message