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Virtuals types #7576

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scabug opened this issue Jun 13, 2013 · 4 comments
Closed

Virtuals types #7576

scabug opened this issue Jun 13, 2013 · 4 comments
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@paulp
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2.10.1

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@scabug
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scabug commented Jun 13, 2013

I have two class VA and VB. Each one contains abstract virtual parameter.
Other classes specialize this virtual parameter.
Is it correct, that my method foo(..).. of A1 takes a parameter of type B2 in this solution?
Thanks and best regards

class A1  extends VA{

  type TB=B1


}

class A2  extends VA{

  type TB=B2
}

class B1  extends VB{

  type TA=A1

}

class B2  extends VB{

  type TA=A2
}

object TMain  extends App {

  val a : VA = new A1()
  var b : VB = new B2()

  println(a.foo(b.asInstanceOf[a.TB]))

}

class VA{

  type TB <: VB
  var t : TB = _

  def foo(b : TB) : TB = {
    t = b
    return t
  }

}

class VB {

  type TA <: VA
}
@scabug
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scabug commented Jun 13, 2013

Imported From: https://issues.scala-lang.org/browse/SI-7576?orig=1
Reporter: kathykiseleva (ketud)
Affected Versions: 2.10.1
Attachments:

  • src.zip (created on Jun 13, 2013 3:05:52 PM UTC, 1503 bytes)

@scabug
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scabug commented Jun 13, 2013

@paulp said (edited on Jun 13, 2013 5:46:17 PM UTC):
"asInstanceOf" means "I know what I'm doing." The method is not accepting a B2. You are lying and saying a B2 is the type it expects.

@scabug scabug closed this as completed Jun 13, 2013
@scabug
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scabug commented Jun 14, 2013

kathykiseleva (ketud) said:
ok, execuse me, I am a begginer in scala:

if I understand good, it means that I can lie and it wouldn't be stopped even by executor. That's why I can execute this method with parameter of type B2...

because I've tested this:
val s : String = "abs"
val n : Int = 5
println(n + s.asInstanceOf[Int])
and during the execution it generates an error

thank you in advance

@scabug
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scabug commented Jun 14, 2013

@paulp said:
That's correct, you can tell any lie you want and the compiler will believe it. As soon as you call "asInstanceOf", the compiler is off the hook.

@scabug scabug added this to the 2.10.1 milestone Apr 7, 2017
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