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much better return type for Iterable.sequence()

See original GitHub issue

Today, @jvasileff figured out the solution to a problem that has bugged us for years — how to assign the correct return type to Iterable.sequence() for known-nonempty streams.

The return type is:

[Element+] | []&Iterable<Element,Absent>

There would be one big problem with making this change, and one much smaller problem:

It would involve a binary-incompatible change to the return type of Iterable.sequence(), which at the Java level would widen from Sequential<? extends Element> to Object.
For the case of an empty stream, that is not something special like [], "", or {}, calling sequence() would result in a reified check of the type argument Absent.

Problem (1) is rather easy to fix with a little hack to the compiler backend to preserve the previous return type Sequential<? extends Element>.

Problem (2) is not so easy to fix, but may not be a big deal.

Issue Analytics

State:
Created 7 years ago
Comments:27 (27 by maintainers)

Top GitHub Comments

1reaction

gavinkingcommented, Dec 7, 2016

That’s really nice!

Type functions FTW.

0reactions

xkr47commented, Feb 24, 2017

Amazing, great!

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