Dependent type is not working in Scala version 3.3.0-RC3

[chungonn]

Compiler version 3.3.0-RC3 and 3.3.1-nightly version

Minimized code

The code works from Scala 3.1.x up to 3.2.2
inline def foo[A](inline a: A)(fn: a.type => String): String =
fn(a)

@main def hello() =
val x= foo("hello")( (s: "hello") => s + " world!")
println(s"x = ${x}")

val y = foo(1)((s: 1) => s + " world!")
println(s"y = ${y}")

println("hello, world")

Output

[error] -- [E083] Type Error: /home/chungonn/development/experiments/scala3test/src/main/scala/Main.scala:2:35 
[error] 2 |inline def foo[A](inline a: A)(fn: a.type => String): String =
[error]   |                                   ^^^^^^
[error]   |  (a : A) is not a valid singleton type, since it is not an immutable path
[error]   |
[error]   | longer explanation available when compiling with `-explain`
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 0 s, completed 30 Mar 2023, 11:26:36 am

Expectation

x = hello world!
y = 1 world!

[SethTisue]

duplicate of #16804?

[chungonn]

duplicate of #16804?

I does seems like the same bug. I am not sure how compiler interprets between a regular parameter list compared a implicit parameter list.

Also the above will compile, if the inline keyword is removed from the first parameter list

[SethTisue]

@chungonn you can try it out in the current nightly build — scala-cli -S 3.nightly, or see https://stackoverflow.com/a/40622879/86485

[chungonn]

@chungonn you can try it out in the current nightly build — scala-cli -S 3.nightly, or see https://stackoverflow.com/a/40622879/86485

@SethTisue I have not tried scala-cli, I only SBT instead for all my Scala work/projects.

I went to the dotty site https://dotty.epfl.ch/ to pick up the nightly build - 3.3.1-RC1-bin-20230328-5c2efc5-NIGHTLY and it is still not working. Should I try to use tmr's nightly build instead?

[chungonn]

@chungonn you can try it out in the current nightly build — scala-cli -S 3.nightly, or see https://stackoverflow.com/a/40622879/86485

I tried it with scala-cli repl, it is still not working

`➜ ~ scala-cli repl -S 3.3.nightly

Downloading JVM temurin:17
Welcome to Scala 3.3.1-RC1-bin-20230328-5c2efc5-NIGHTLY-git-5c2efc5 (17.0.6, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> inline def foo[A](inline a: A)(fn: a.type => String): String =
| fn(a)
|
-- [E083] Type Error: ----------------------------------------------------------
1 |inline def foo[A](inline a: A)(fn: a.type => String): String =
| ^^^^^^
| (a : A) is not a valid singleton type, since it is not an immutable path
|
| longer explanation available when compiling with -explain
1 error found
`

[SethTisue]

@chungonn I'm sorry, I was moving too quickly and my suggestion to try it in the nightly build was not really relevant.

the resolution of #16804 is that the code in question should not compile — see Nicolas's remarks. it seems to me that your code should not compile either, unless you're trying to make a case otherwise?

[SethTisue]

(as an aside, in the future, should you want to use a Scala 3 nightly in sbt rather than scala-cli, see the Stack Overflow link I provided — that's why I included it)

[chungonn]

(as an aside, in the future, should you want to use a Scala 3 nightly in sbt rather than scala-cli, see the Stack Overflow link I provided — that's why I included it)

Yes, I went to the link and saw your post. I wasn't sure how to setup in SBT for Scala 3. Then I read your notes on the use scala-cli, then I installed scala-cli and followed the instructions given.

Thanks for pointing to that link though

[chungonn]

@chungonn I'm sorry, I was moving too quickly and my suggestion to try it in the nightly build was not really relevant.

the resolution of #16804 is that the code in question should not compile — see Nicolas's remarks. it seems to me that your code should not compile either, unless you're trying to make a case otherwise?

Yes, my code is not compiling. The case I am raising here is, the same code works for Scala 3.2.x and versions before it. Also the example I provided above shows that the argument constants.

I am confused by Nicolas's remarks, He remarked that that it is a bug, and was fixed in issue #15511 . However, he followed by an example why it should not have worked, as his examples demonstrated the creating new instances of X. I my example, I used 2 singleton types "hello" and 1.

I would assume that my case was incorrectly working prior to Scala 3.3.x, and now from Scala 3.3.x onwards, it is correctly not working, am I right?

[chungonn]

I have removed the inline keyword from the parameter list and all is compiling. I hope that rest of the app which uses the library will not have problems.

Should I close this issue now?

[SethTisue]

I would assume that my case was incorrectly working prior to Scala 3.3.x, and now from Scala 3.3.x onwards, it is correctly not working, am I right?

that is my understanding

@nicolasstucki can you close the issue if you agree?

[chungonn]

My apologies, I was in a huge rush yesterday that I just realized my sample code was being commented out hence it was not showing i.e. showing only the last line which is the output. I have edited the issue to uncomment the sample code, it is correctly showing.

[odersky]

OK, I think we can close this now. Good that it was cleared up.