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FAQ: revise entry on Scala versionNumberString #2482

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19 changes: 12 additions & 7 deletions _overviews/FAQ/index.md
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Expand Up @@ -108,20 +108,25 @@ Your sbt 1.x build definition is always a Scala 2.12 program.
Regardless, in your `build.sbt`, you can set `scalaVersion` to whichever
available distribution you want and your program code will be compiled with that version.

### I want Scala 3.1.1 (etc); why does std lib say it's using Scala 2.13?
### I want Scala 3. Why does `versionNumberString` say I'm on 2.13?

Scala 3 currently uses the Scala 2.13 library by leveraging its seamless
interoperability. Note that it does not necessarily ingest the latest
version of the Scala 2.13 library.
To aid migration, Scala 3 currently uses the Scala 2.13 library as-is,
with only minor supplements. That's why `versionString` and
`versionNumberString` report that Scala 2 is in use:

```
Welcome to Scala 3.1.1 (17.0.2, Java OpenJDK 64-Bit Server VM).
Welcome to Scala 3.1.3 (17.0.3, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> util.Properties.versionString
val res0: String = version 2.13.6
scala> util.Properties.versionNumberString
val res0: String = 2.13.8
```

Note that Scala 3 offers
`dotty.tools.dotc.config.Properties.versionNumberString`, but only if
you have scala3-compiler on the classpath. So that works in the Scala 3
REPL, but won't work in typical Scala 3 application code.

### Why is my (abstract or overridden) `val` null?

<!-- this is left over from a previous version of the FAQ.
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