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Commit 77c30e5

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CC Language Reference Improvements v2 (#23818)
2 parents 17f1803 + 6e6cf79 commit 77c30e5

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‎docs/_docs/reference/experimental/capture-checking/how-to-use.md‎

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@@ -6,7 +6,48 @@ nightlyOf: https://docs.scala-lang.org/scala3/reference/experimental/capture-che
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## Enabling Capture Checking
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TODO
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Use Scala 3 nightly for the latest features and fixes.
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Add this import in any file that uses capture checking:
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```scala
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import language.experimental.captureChecking
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```
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### Separation Checking
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Requires the import above:
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```scala
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import language.experimental.captureChecking
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import language.experimental.separationChecking
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```
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### SBT Project Template
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Alternatively, you can clone a pre-defined SBT project to get
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started: https://github.com/lampepfl/scala3-cc-template
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### The REPL/Scala-CLI
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Using the command line through explicit parameters:
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```bash
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scala -S 3.nightly -language:experimental.captureChecking
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```
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or when reading from a file:
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```scala
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// foo.scala:
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//> using scala 3.nightly
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import language.experimental.captureChecking
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...
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```
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Then, it suffices to run
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```bash
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scala foo.scala
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```
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## API Documentation
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Scaladoc supports capture checking. The nightly standard library API docs have it enabled by default:
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https://nightly.scala-lang.org/api/
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## Compilation Options
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-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/classifiers-secondclass.scala:41:28 ----------------------
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41 | parReduce(1 to 1000): (a, b) => // error
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| ^
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|Found: (a: Int, b: Int) ->{f.write, f.read} Int
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|Required: (Int, Int) ->{cap.only[Read]} Int
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|
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|Note that capability f.write is not included in capture set {cap.only[Read]}.
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|
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|where: cap is a fresh root capability created in anonymous function of type (f2: Levels.File^): Unit when checking argument to parameter op of method parReduce
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42 | f.write(42) // the error stems from here
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43 | a + b + f.read() // ok
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|
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| longer explanation available when compiling with `-explain`
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-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/classifiers-secondclass.scala:53:30 ----------------------
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53 | parReduce(1 to 1000): (a, b) => // error
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| ^
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|Found: (a: Int, b: Int) ->{f.write, f.read, g.read} Int
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|Required: (Int, Int) ->{cap.only[Read]} Int
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|
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|Note that capability f.write is not included in capture set {cap.only[Read]}.
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|
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|where: cap is a fresh root capability created in anonymous function of type (g2: Levels.File^): Unit when checking argument to parameter op of method parReduce
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54 | f.write(42) // the error stems from here
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55 | a + b + f.read() + g.read() // ok
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|
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| longer explanation available when compiling with `-explain`
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-- [E007] Type Mismatch Error: tests/neg-custom-args/captures/classifiers-secondclass.scala:56:30 ----------------------
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56 | parReduce(1 to 1000): (a, b) => // error
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| ^
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|Found: (a: Int, b: Int) ->{g.write} Int
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|Required: (Int, Int) ->{cap.only[Read]} Int
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|
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|Note that capability g.write is not included in capture set {cap.only[Read]}.
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|
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|where: cap is a fresh root capability created in anonymous function of type (g2: Levels.File^): Unit when checking argument to parameter op of method parReduce
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57 | g.write(42) // the error stems from here
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58 | 0
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|
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| longer explanation available when compiling with `-explain`
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@@ -1,67 +1,61 @@
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import language.experimental.captureChecking
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import language.experimental.separationChecking
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import language.experimental.erasedDefinitions
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import caps.*
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// Test inspired by the "Gentrification Gone too Far?" paper
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object Levels:
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/* User-defined capability classifiers */
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trait Read extends Classifier, SharedCapability
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trait ReadWrite extends Classifier, SharedCapability
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trait File(val name: String):
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val r: Read^
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val rw: ReadWrite^
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// operations guarded by boxed capability members
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// file-specific capability members, these are ensured to be erased
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erased val r: Read^
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erased val rw: ReadWrite^
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// operations guarded by capability members
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val read: () ->{r} Int
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val write: Int ->{rw} Unit
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object File:
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def apply(s: String): File^ = new File(s) {
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val r = new Read {}
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val rw = new ReadWrite {}
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erased val r = new Read {}
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erased val rw = new ReadWrite {}
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val read = () =>
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println(s"Reading from $name with capability $r")
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val write = (i: Int) =>
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println(s"Writing $i to $name with capability $rw")
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}
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// Unfortunately, we do not have @use lambdas yet
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trait UseFunction[U]:
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def apply[C^](f: File^{C}): U
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def withFile[U](name: String)(block: UseFunction[U]): U = block(File(name)) // unrestricted use of files & other capabilities
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def withFile[U](name: String)(block: File^ => U): U = block(File(name)) // unrestricted use of files & other capabilities
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def parReduce[U](xs: Seq[U])(op: (U, U) ->{cap.only[Read]} U): U = xs.reduce(op) // only Read-classified allowed
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@main def test =
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withFile("foo.txt"):
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new UseFunction[Unit]:
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def apply[C^](f: File^{C}): Unit =
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f.read() // ok
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parReduce(1 to 1000): (a, b) =>
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a * b * f.read() // ok
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parReduce(1 to 1000): (a, b) => // error
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f.write(42) // the error stems from here
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a + b + f.read() // ok
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f.write(42) // ok, unrestricted access to file
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withFile("foo.txt"): f =>
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f.read() // ok
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parReduce(1 to 1000): (a, b) =>
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a * b * f.read() // ok
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parReduce(1 to 1000): (a, b) => // error
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f.write(42) // the error stems from here
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a + b + f.read() // ok
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f.write(42) // ok, unrestricted access to file
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def testMulti =
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withFile("foo.txt"):
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new UseFunction[Unit]:
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def apply[C^](f: File^{C}): Unit =
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withFile("bar.txt"):
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new UseFunction[Unit]:
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def apply[C^](g: File^{C}): Unit =
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f.read() // ok
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g.read() // ok
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parReduce(1 to 1000): (a, b) =>
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a * b * f.read() + g.read() // ok
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parReduce(1 to 1000): (a, b) => // error
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f.write(42) // the error stems from here
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a + b + f.read() + g.read() // ok
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parReduce(1 to 1000): (a, b) => // error
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g.write(42) // the error stems from here
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0
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f.write(42) // ok, unrestricted access to file
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g.write(42) // ok, unrestricted access to file
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withFile("foo.txt"): f =>
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withFile("bar.txt"): g =>
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f.read() // ok
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g.read() // ok
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parReduce(1 to 1000): (a, b) =>
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a * b * f.read() + g.read() // ok
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parReduce(1 to 1000): (a, b) => // error
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f.write(42) // the error stems from here
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a + b + f.read() + g.read() // ok
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parReduce(1 to 1000): (a, b) => // error
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g.write(42) // the error stems from here
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0
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f.write(42) // ok, unrestricted access to file
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g.write(42) // ok, unrestricted access to file
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