Question: Singleton Seq of Array

[danieldietrich]

Hi Lukas,

I'm not convinced about the java.util.stream.Stream.of() API. There are

• Stream.of(T t) respectively Seq.of(T t)
• Stream.of(T... values) respectively Seq.of(T... values)

which does not allow us to create a Stream/Seq of an Array, i.e.

• Seq.of(new String[] { "hello" }) is a Seq<String> instead of a Seq<String[]>

Workaround:

• Seq.of(new String[][]{{ "" }}), which is ugly

Just want to hear your opinion about the practical value of having a special API for a singleton Array Seq.

And also: What is the use case for a Stream.of(T t). If there would be only a Stream.of(T... values) we could also call Stream.of(t)!? Looking at the implementation of java.util.stream.Stream.of(T t) I see a difference, but from the API perspective I don't see the point.

- Daniel

[lukaseder]

Just want to hear your opinion about the practical value of having a special API for a singleton Array Seq.

It's simple. The use-case of Seq.of(1, 2, 3, 4, 5) is just more useful and common than the use-case of Seq.of(new String[][] {{ "" }}). So, this API is a compromise worth making, although I see your point. Another workaround:

Seq.of((Object) new String[] { "" });

Looking at the implementation of java.util.stream.Stream.of(T t) I see a difference, but from the API perspective I don't see the point.

Less pressure on the GC due to unneeded array references? EnumSet.of(...) took this even further

[danieldietrich]

Thanks, I thought I've overseen s.th.

I like varargs, too. A little bit nasty is the need for @Safeargs and @SuppressWarnings("unchecked") in general (for API designers).

An alternative for creating a singleton would be another method name, like Seq.singleton(String[] { "" }). However, Seq reflects the java Stream API and I think here is nothing to do.

My question is clarified, the issue can be closed :-)

Thanks again!

• Daniel

[lukaseder]

A little bit nasty is the need for @SafeVarargs

You're telling me? I'm maintaining a huge Java-6 compatible API (jOOQ). I could kick someone for not having introduced @SafeVarargs any earlier :-) (and in a better way)

An alternative for creating a singleton would be another method name, like Seq.singleton

Yes, that would match the existing java.util.Collections.singleton().

However, Seq reflects the java Stream API and I think here is nothing to do.

Yes. Good enough for "us". You can do better, in Javaslang :-)

[danieldietrich]

That's fair enough :-)

[lukaseder]

I've just thought of another reason why you should overload method(T) and method(T...):
http://blog.jooq.org/2014/09/19/learn-how-nashorn-prevents-effective-api-evolution-on-a-new-level/

[danieldietrich]

Thank you for sharing! That was insightful, there is so much to learn!

Also interesting how deep and thoughtful little things are which seem to be trivial at first sight.

[jbgi]

I think the proper work around is
Stream.<String[]> of(new String[] { "hello" });

[lukaseder]

@jbgi: Yes, you're right

[danieldietrich]

@jbgi it is 6 chars longer than Stream.of(new String[][]{{"hello"}}); but way less ugly :-)

[danieldietrich]

Just for the sake of completeness:

And also: What is the use case for a Stream.of(T t). If there would be only a Stream.of(T... values) we could also call Stream.of(t)!? Looking at the implementation of java.util.stream.Stream.of(T t) I see a difference, but from the API perspective I don't see the point.

It's the null - Stream.of(T... values) throws when called with null arg.

[lukaseder]

It's the null - Stream.of(T... values) throws when called with null arg.

Interesting point, I haven't thought of this... This is probably relevant only when passing a null literal such as of(null), though, which should intuitively correspond to of((Object) null), but of course doesn't, really meaning of((Object[]) null)