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Merge pull request #8776 from dotty-staging/add-main-proto
Prototype for proposed main method generation scheme
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11 files changed

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‎compiler/src/dotty/tools/dotc/transform/TypeTestsCasts.scala‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -220,16 +220,17 @@ object TypeTestsCasts {
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* can be true in some cases. Issues a warning or an error otherwise.
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*/
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def checkSensical(foundClasses: List[Symbol])(using Context): Boolean =
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def exprType = i"type ${expr.tpe.widen.stripAnnots}"
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def check(foundCls: Symbol): Boolean =
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if (!isCheckable(foundCls)) true
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else if (!foundCls.derivesFrom(testCls)) {
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val unrelated = !testCls.derivesFrom(foundCls) && (
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testCls.is(Final) || !testCls.is(Trait) && !foundCls.is(Trait)
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)
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if (foundCls.is(Final))
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unreachable(i"type ${expr.tpe.widen} is not a subclass of $testCls")
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unreachable(i"$exprType is not a subclass of $testCls")
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else if (unrelated)
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unreachable(i"type ${expr.tpe.widen} and $testCls are unrelated")
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unreachable(i"$exprType and $testCls are unrelated")
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else true
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}
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else true
@@ -238,7 +239,7 @@ object TypeTestsCasts {
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val foundEffectiveClass = effectiveClass(expr.tpe.widen)
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if foundEffectiveClass.isPrimitiveValueClass && !testCls.isPrimitiveValueClass then
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ctx.error("cannot test if value types are references", tree.sourcePos)
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ctx.error(i"cannot test if value of $exprType is a reference of $testCls", tree.sourcePos)
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false
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else foundClasses.exists(check)
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end checkSensical

‎tests/pos/main-method-scheme-class-based.scala‎

Lines changed: 205 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,205 @@
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import annotation.StaticAnnotation
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import collection.mutable
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/** MainAnnotation provides the functionality for a compiler-generated main class.
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* It links a compiler-generated main method (call it compiler-main) to a user
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* written main method (user-main).
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* The protocol of calls from compiler-main is as follows:
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*
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* - create a `command` with the command line arguments,
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* - for each parameter of user-main, a call to `command.argGetter`,
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* or `command.argsGetter` if is a final varargs parameter,
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* - a call to `command.run` with the closure of user-main applied to all arguments.
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*/
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trait MainAnnotation extends StaticAnnotation:
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/** The class used for argument string parsing. E.g. `scala.util.FromString`,
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* but could be something else
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*/
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type ArgumentParser[T]
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/** The required result type of the main function */
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type MainResultType
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/** A new command with arguments from `args` */
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def command(args: Array[String]): Command
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/** A class representing a command to run */
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abstract class Command:
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/** The getter for the next argument of type `T` */
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def argGetter[T](argName: String, fromString: ArgumentParser[T], defaultValue: Option[T] = None): () => T
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/** The getter for a final varargs argument of type `T*` */
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def argsGetter[T](argName: String, fromString: ArgumentParser[T]): () => Seq[T]
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/** Run `program` if all arguments are valid,
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* or print usage information and/or error messages.
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*/
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def run(program: => MainResultType, progName: String, docComment: String): Unit
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end Command
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end MainAnnotation
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//Sample main class, can be freely implemented:
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class main extends MainAnnotation:
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type ArgumentParser[T] = util.FromString[T]
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type MainResultType = Any
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def command(args: Array[String]): Command = new Command:
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/** A buffer of demanded argument names, plus
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* "?" if it has a default
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* "*" if it is a vararg
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* "" otherwise
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*/
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private var argInfos = new mutable.ListBuffer[(String, String)]
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/** A buffer for all errors */
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private var errors = new mutable.ListBuffer[String]
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/** Issue an error, and return an uncallable getter */
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private def error(msg: String): () => Nothing =
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errors += msg
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() => assertFail("trying to get invalid argument")
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/** The next argument index */
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private var argIdx: Int = 0
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private def argAt(idx: Int): Option[String] =
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if idx < args.length then Some(args(idx)) else None
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private def nextPositionalArg(): Option[String] =
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while argIdx < args.length && args(argIdx).startsWith("--") do argIdx += 2
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val result = argAt(argIdx)
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argIdx += 1
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result
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private def convert[T](argName: String, arg: String, p: ArgumentParser[T]): () => T =
80+
p.fromStringOption(arg) match
81+
case Some(t) => () => t
82+
case None => error(s"invalid argument for $argName: $arg")
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def argGetter[T](argName: String, p: ArgumentParser[T], defaultValue: Option[T] = None): () => T =
85+
argInfos += ((argName, if defaultValue.isDefined then "?" else ""))
86+
val idx = args.indexOf(s"--$argName")
87+
val argOpt = if idx >= 0 then argAt(idx + 1) else nextPositionalArg()
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argOpt match
89+
case Some(arg) => convert(argName, arg, p)
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case None => defaultValue match
91+
case Some(t) => () => t
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case None => error(s"missing argument for $argName")
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94+
def argsGetter[T](argName: String, p: ArgumentParser[T]): () => Seq[T] =
95+
argInfos += ((argName, "*"))
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def remainingArgGetters(): List[() => T] = nextPositionalArg() match
97+
case Some(arg) => convert(arg, argName, p) :: remainingArgGetters()
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case None => Nil
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val getters = remainingArgGetters()
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() => getters.map(_())
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def run(f: => MainResultType, progName: String, docComment: String): Unit =
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def usage(): Unit =
104+
println(s"Usage: $progName ${argInfos.map(_ + _).mkString(" ")}")
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def explain(): Unit =
107+
if docComment.nonEmpty then println(docComment) // todo: process & format doc comment
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def flagUnused(): Unit = nextPositionalArg() match
110+
case Some(arg) =>
111+
error(s"unused argument: $arg")
112+
flagUnused()
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case None =>
114+
for
115+
arg <- args
116+
if arg.startsWith("--") && !argInfos.map(_._1).contains(arg.drop(2))
117+
do
118+
error(s"unknown argument name: $arg")
119+
end flagUnused
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if args.isEmpty || args.contains("--help") then
122+
usage()
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explain()
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else
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flagUnused()
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if errors.nonEmpty then
127+
for msg <- errors do println(s"Error: $msg")
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usage()
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else f match
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case n: Int if n < 0 => System.exit(-n)
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case _ =>
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end run
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end command
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end main
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// Sample main method
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object myProgram:
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/** Adds two numbers */
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@main def add(num: Int, inc: Int = 1): Unit =
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println(s"$num + $inc = ${num + inc}")
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end myProgram
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// Compiler generated code:
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object add extends main:
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def main(args: Array[String]) =
150+
val cmd = command(args)
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val arg1 = cmd.argGetter[Int]("num", summon[ArgumentParser[Int]])
152+
val arg2 = cmd.argGetter[Int]("inc", summon[ArgumentParser[Int]], Some(1))
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cmd.run(myProgram.add(arg1(), arg2()), "add", "Adds two numbers")
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end add
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/** --- Some scenarios ----------------------------------------
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> java add 2 3
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2 + 3 = 5
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> java add 4
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4 + 1 = 5
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> java add --num 10 --inc -2
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10 + -2 = 8
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> java add --num 10
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10 + 1 = 11
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> java add --help
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Usage: add num inc?
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Adds two numbers
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> java add
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Usage: add num inc?
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Adds two numbers
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> java add 1 2 3 4
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Error: unused argument: 3
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Error: unused argument: 4
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Usage: add num inc?
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> java add -n 1 -i 10
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Error: invalid argument for num: -n
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Error: unused argument: -i
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Error: unused argument: 10
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Usage: add num inc?
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> java add --n 1 --i 10
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Error: missing argument for num
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Error: unknown argument name: --n
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Error: unknown argument name: --i
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Usage: add num inc?
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> java add true 10
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Error: invalid argument for num: true
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Usage: add num inc?
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> java add true false
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Error: invalid argument for num: true
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Error: invalid argument for inc: false
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Usage: add num inc?
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> java add true false 10
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Error: invalid argument for num: true
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Error: invalid argument for inc: false
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Error: unused argument: 10
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Usage: add num inc?
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> java add --inc 10 --num 20
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20 + 10 = 30
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> java add binary 10 01
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Error: invalid argument for num: binary
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Error: unused argument: 01
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Usage: add num inc?
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*/

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