Add an immutable array type #5885

odersky · 2019-02-09T12:26:20Z

So far, it's called scala.IArray[T]. I am not super happy with the name but could not come up with anything better yet.

It's an opaque alias of Array[T] that only exposes the apply and length methods.

Still missing: Wrappers that add all sequence ops to IArrays. We should upgrade to the new collections before we do this.

odersky · 2019-02-09T13:23:52Z

Btw, the first lines of IArray.scala af2a0e6 are a great showcase how opaque types, implied instances, extension methods, toplevel definitions, and inline can work together to give something beautiful.

julienrf · 2019-02-09T19:36:20Z

tests/run/iarrays.scala

+
+  val xs = IArray(1, 2, 3)
+
+  def f[T](ys: IArray[T]) = {


What type does this method erase to? f(ys: Array[AnyRef])? Or f(ys: AnyRef)?

No, it's Object. Just what Array[T] erases to.

odersky · 2019-02-11T16:19:41Z

I tried to make IArray covariant, using

opaque type IArray[+T] = Array[_ <: T]

Unfortunately, that runs into problems when it comes to class tags. I get:

[error] 30 |  def concat[T: ClassTag](xss: IArray[T]*): IArray[T] = Array.concat(xss: _*)
[error]    |                                                                             ^
[error]    |                              No ClassTag available for Array[_ <: T]#T'
[error]    |                              
[error]    |                              where:    T  is a type in method concat
[error]    |                                        T' is a type in class Array
[error] one error found

Indeed, there's no way to create an Array[_ <: T]. There are probably ways around this, using casts. But it makes me wary to try this as the official definition of IArray. IArray[T] should just work out of the box, in exactly the same way Array[T] does. But, Array[T] and Array[_ <: T] are not equivalent in all contexts.

sjrd · 2019-02-12T09:23:43Z

That shouldn't matter outside of the companion of IArray, though. Outside, the only thing that can be seen is IArray[T], not any Array[_ <: T]. We might require a few hoops inside the definition of IArray, but none of that is going to leak outside.

odersky · 2019-02-14T13:10:56Z

@sjrd Right. After adding some casts in iArray's implementation, I could make them covariant, after all. 👍

library/src-bootstrapped/scala/IArray.scala

julienrf · 2019-02-19T13:31:47Z

tests/pos/covaraint-opqaue.scala

@@ -0,0 +1,3 @@
+import annotation.unchecked.uncheckedVariance


Typo in the file name: “covariant-opaque.scala”

julienrf · 2019-02-19T13:33:20Z

tests/run/iarrays.scala

+  val bs: IArray[Double] = IArray(1.0, 2.0)
+  val cs: Array[Double] = bs.asInstanceOf[Array[Double]]
+  cs(1) = 3.0
+  assert(bs(1) == 3.0)


Can we also check that apply and update don’t box elements?

That's harder. I believe there are ways to test it, but I don't know them. The fact that apply is an inline method means it is literally replaced by its right-hand side, so by the rules of inlining there can't be any boxing. I verified the code after erasure by looking at it to make sure that's the case.

odersky · 2019-02-22T15:18:10Z

Community build fails with:

Fetching latest Dotty nightly version...
Latest Dotty nightly build version: 0.14.0-bin-20190221-daf4ce9-NIGHTLY
[info] Set current project to squants (in build file:/tmp/3/community-build/community-projects/squants/)
[info] Forcing Scala version to 0.14.0-bin-SNAPSHOT on all projects.
[info] Reapplying settings...
[info] Set current project to squants (in build file:/tmp/3/community-build/community-projects/squants/)
[info] Updating squantsJVM...
[error] Unable to find credentials for [Sonatype Nexus Repository Manager @ oss.sonatype.org].
[warn] CLIENT ERROR: 401 Unauthorized. Check your resolvers username and password.

/cc @OlivierBlanvillain

OlivierBlanvillain · 2019-02-22T15:30:32Z

Are the changes to the community build submodules in c7b0651 intentional?

Unary extension methods are inlined before the end of `extMethodApply`. Have to take this into account when checking that the call is to an extension method.

IArray[T] is an opaque alias for Array[T]

This gives us the right error message if we try to instantiate an hk opaque type with `new`.

Also, add `empty` method.

odersky · 2019-02-22T16:18:34Z

@OlivierBlanvillain No, I discovered my error: pushed wrong submodule hashes.

Need to drop the explicit result type since apparently Array's unapplySeq type is different between 2.12 and 2.13.

odersky · 2019-02-23T10:53:25Z

Going to merge this now, to avoid further breakage by fast-moving infrastructure changes.

odersky force-pushed the add-immutable-array branch from a96c5a3 to 1783f42 Compare February 9, 2019 12:30

odersky requested a review from julienrf February 9, 2019 12:35

odersky assigned julienrf Feb 9, 2019

julienrf reviewed Feb 9, 2019

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odersky force-pushed the add-immutable-array branch from 1783f42 to f0eb2bb Compare February 14, 2019 13:09

julienrf reviewed Feb 18, 2019

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library/src-bootstrapped/scala/IArray.scala Outdated Show resolved Hide resolved

odersky force-pushed the add-immutable-array branch from 1e8f916 to 4f98732 Compare February 19, 2019 12:40

julienrf reviewed Feb 19, 2019

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odersky force-pushed the add-immutable-array branch 2 times, most recently from bbca7f0 to c7b0651 Compare February 22, 2019 14:12

odersky added 12 commits February 22, 2019 17:11

Handle @uncheckedVariance in hk-types

a64c7cd

Fix bug related to inlined unary extension methods

408cec1

Unary extension methods are inlined before the end of `extMethodApply`. Have to take this into account when checking that the call is to an extension method.

Add immutable array type

da2c0de

IArray[T] is an opaque alias for Array[T]

Add test for uncheckedVariance in hk types

f1645d4

Make IArray covariant

44f6142

Fix underlyingClassRef for hk types

0dcb5e8

This gives us the right error message if we try to instantiate an hk opaque type with `new`.

Test IArray[Any]

a0104fd

More tests

ea4ba34

Fix and add comments

36e3b0f

Also, add `empty` method.

Add representation test

c2a3ccd

fix typo in file name

6bf73a9

Fix typo

c532d3e

odersky force-pushed the add-immutable-array branch from c7b0651 to c532d3e Compare February 22, 2019 16:15

Make IArray.unapplySeq cross build for 2.12/2.13.

b9decdc

Need to drop the explicit result type since apparently Array's unapplySeq type is different between 2.12 and 2.13.

odersky force-pushed the add-immutable-array branch from a8b794c to b9decdc Compare February 23, 2019 08:46

odersky merged commit 63ce36a into scala:master Feb 23, 2019

allanrenucci deleted the add-immutable-array branch February 24, 2019 11:31

biboudis added this to the 0.14 Tech Preview milestone Apr 5, 2019

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Add an immutable array type #5885

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		@@ -0,0 +1,3 @@
		import annotation.unchecked.uncheckedVariance

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