Add Seq.indexOf method(s)

[tlinkowski]

Since we have Seq.contains and Seq.get(index), it'd be nice to also have long indexOf(T item) or OptionalLong indexOf(T item).

Incidentally, we could also have long/OptionalLong indexOf(Predicate<? super T> predicate) which would be equivalent to Guava's Iterators.indexOf.

[lukaseder]

Excellent idea. I agree with both proposed APIs:

OptionalLong indexOf(T item)
OptionalLong indexOf(Predicate<? super T> predicate)

The latter is also not unexpected, given the existing Seq.findFirst(Predicate). I think we should prefer OptionalLong over the historic -1 encoding in a primitive long as it fits better into the Stream / Seq API.

Would you be interested in providing a pull request for this?

[amaembo]

I have such methods returning OptionalLong. Returning -1 seems not consistent with other Stream API methods. Though probably a matter of taste.

[tlinkowski]

I am also in favor of OptionalLong.

OK, I'll create a pull request for this over the weekend. I propose an implementation utilizing iterator() and mirroring Guava's Iterators.indexOf.

[lukaseder]

Excellent, looking forward!

[lukaseder]

Implementation in #243