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Fall back to direct subtype comparison at the end in dropIfSuper and dropIfSub (#20523)
Improve compiling in #20516. We need to be careful to check branches of AndTypes and OrTypes in correct order, see discussion in issue #20516. Fall back to direct subtype comparison at the end in dropIfSuper and dropIfSub. We may need to improve subtype checking for large intersections further to be able to fully test the example.
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‎compiler/src/dotty/tools/dotc/core/TypeComparer.scala‎

Lines changed: 6 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -2535,36 +2535,28 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
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/** If some (&-operand of) `tp` is a supertype of `sub` replace it with `NoType`.
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*/
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private def dropIfSuper(tp: Type, sub: Type): Type =
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def isSuperOf(sub: Type): Boolean = sub match
2540-
case AndType(sub1, sub2) => isSuperOf(sub1) || isSuperOf(sub2)
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case sub: TypeVar if sub.isInstantiated => isSuperOf(sub.instanceOpt)
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case _ => isSubTypeWhenFrozen(sub, tp)
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// We need to be careful to check branches of AndTypes and OrTypes in correct order,
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// see discussion in issue #20516.
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tp match
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case tp @ AndType(tp1, tp2) =>
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recombine(dropIfSuper(tp1, sub), dropIfSuper(tp2, sub), tp)
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case tp: TypeVar if tp.isInstantiated =>
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dropIfSuper(tp.instanceOpt, sub)
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case _ =>
2550-
if isSuperOf(sub) then NoType else tp
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if isSubTypeWhenFrozen(sub, tp) then NoType else tp
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end dropIfSuper
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/** If some (|-operand of) `tp` is a subtype of `sup` replace it with `NoType`. */
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private def dropIfSub(tp: Type, sup: Type, canConstrain: Boolean): Type =
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def isSubOf(sup: Type): Boolean = sup match
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case OrType(sup1, sup2) => isSubOf(sup1) || isSubOf(sup2)
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case sup: TypeVar if sup.isInstantiated => isSubOf(sup.instanceOpt)
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case _ => isSubType(tp, sup, whenFrozen = !canConstrain)
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// We need to be careful to check branches of AndTypes and OrTypes in correct order,
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// see discussion in issue #20516.
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tp match
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case tp @ OrType(tp1, tp2) =>
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recombine(dropIfSub(tp1, sup, canConstrain), dropIfSub(tp2, sup, canConstrain), tp)
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case tp: TypeVar if tp.isInstantiated =>
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dropIfSub(tp.instanceOpt, sup, canConstrain)
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case _ =>
2567-
if isSubOf(sup) then NoType else tp
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if isSubType(tp, sup, whenFrozen = !canConstrain) then NoType else tp
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end dropIfSub
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/** There's a window of vulnerability between ElimByName and Erasure where some

‎tests/pos-deep-subtype/i20516.scala‎

Lines changed: 205 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,205 @@
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object Main {
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trait A {}
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trait B {}
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trait C {}
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trait D {}
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trait E {}
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trait F {}
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trait G {}
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trait H {}
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trait I {}
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trait J {}
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trait K {}
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trait L {}
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trait M {}
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trait N {}
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trait O {}
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trait P {}
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trait Q {}
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trait R {}
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trait S {}
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trait T {}
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trait U {}
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trait V {}
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trait W {}
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trait X {}
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trait Y {}
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trait Z {}
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type AlphabeticServices = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutA = B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutB = A & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutC = A & B & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutD = A & B & C & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutE = A & B & C & D & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutF = A & B & C & D & E & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutG = A & B & C & D & E & F & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutH = A & B & C & D & E & F & G & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutI = A & B & C & D & E & F & G & H & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutJ = A & B & C & D & E & F & G & H & I & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutK = A & B & C & D & E & F & G & H & I & J & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutL = A & B & C & D & E & F & G & H & I & J & K & M & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutM = A & B & C & D & E & F & G & H & I & J & K & L & N & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutN = A & B & C & D & E & F & G & H & I & J & K & L & M & O & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutO = A & B & C & D & E & F & G & H & I & J & K & L & M & N & P & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutP = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & Q & R & S & T & U & V & W & X & Y & Z
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type EnvOutQ = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & R & S & T & U & V & W & X & Y & Z
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type EnvOutR = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & S & T & U & V & W & X & Y & Z
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type EnvOutS = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & T & U & V & W & X & Y & Z
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type EnvOutT = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & U & V & W & X & Y & Z
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type EnvOutU = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & V & W & X & Y & Z
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type EnvOutV = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & W & X & Y & Z
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type EnvOutW = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & X & Y & Z
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type EnvOutX = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & Y & Z
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type EnvOutY = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Z
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type EnvOutZ = A & B & C & D & E & F & G & H & I & J & K & L & M & N & O & P & Q & R & S & T & U & V & W & X & Y
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trait Reader[-E, A] {
59+
def map[B](f: A => B): Reader[E, B] = ???
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def flatMap[E2 <: E, B](f: A => Reader[E2, B]): Reader[E2, B] = ???
61+
}
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def e1: Reader[EnvOutA, Unit] = ???
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def e2: Reader[EnvOutB, Unit] = ???
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def e3: Reader[EnvOutC, Unit] = ???
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def e4: Reader[EnvOutD, Unit] = ???
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def e5: Reader[EnvOutE, Unit] = ???
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def e6: Reader[EnvOutF, Unit] = ???
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def e7: Reader[EnvOutG, Unit] = ???
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def e8: Reader[EnvOutH, Unit] = ???
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def e9: Reader[EnvOutI, Unit] = ???
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def e10: Reader[EnvOutJ, Unit] = ???
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def e11: Reader[EnvOutK, Unit] = ???
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def e12: Reader[EnvOutL, Unit] = ???
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def e13: Reader[EnvOutM, Unit] = ???
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def e14: Reader[EnvOutN, Unit] = ???
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def e15: Reader[EnvOutO, Unit] = ???
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def e16: Reader[EnvOutP, Unit] = ???
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def e17: Reader[EnvOutQ, Unit] = ???
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def e18: Reader[EnvOutR, Unit] = ???
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def e19: Reader[EnvOutS, Unit] = ???
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def e20: Reader[EnvOutT, Unit] = ???
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def e21: Reader[EnvOutU, Unit] = ???
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def e22: Reader[EnvOutV, Unit] = ???
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def e23: Reader[EnvOutW, Unit] = ???
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def e24: Reader[EnvOutX, Unit] = ???
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def e25: Reader[EnvOutY, Unit] = ???
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def e26: Reader[EnvOutZ, Unit] = ???
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90+
def program: Reader[AlphabeticServices, Unit] = for {
91+
//1
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_ <- e1
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_ <- e2
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_ <- e3
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_ <- e4
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_ <- e5
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_ <- e6
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_ <- e7
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_ <- e8
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_ <- e8
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_ <- e9
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_ <- e10
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_ <- e11
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_ <- e12
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_ <- e13
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_ <- e14
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_ <- e15
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_ <- e16
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_ <- e17
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_ <- e18
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_ <- e19
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_ <- e20
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_ <- e21
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_ <- e22
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_ <- e23
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_ <- e24
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_ <- e25
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_ <- e26
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// 2
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_ <- e1
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_ <- e2
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_ <- e3
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_ <- e4
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_ <- e5
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_ <- e6
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_ <- e7
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_ <- e8
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_ <- e8
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_ <- e9
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_ <- e10
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_ <- e11
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_ <- e12
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_ <- e13
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_ <- e14
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_ <- e15
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_ <- e16
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_ <- e17
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_ <- e18
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_ <- e19
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_ <- e20
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_ <- e21
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_ <- e22
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_ <- e23
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_ <- e24
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_ <- e25
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_ <- e26
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// TODO: optimize the subtype checking for large intersection types further
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//3
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// _ <- e1
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// _ <- e2
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// _ <- e3
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// _ <- e4
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// _ <- e5
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// _ <- e6
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// _ <- e7
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// _ <- e8
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// _ <- e8
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// _ <- e9
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// _ <- e10
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// _ <- e11
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// _ <- e12
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// _ <- e13
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// _ <- e14
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// _ <- e15
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// _ <- e16
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// _ <- e17
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// _ <- e18
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// _ <- e19
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// _ <- e20
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// _ <- e21
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// _ <- e22
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// _ <- e23
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// _ <- e24
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// _ <- e25
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// _ <- e26
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// 4
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// _ <- e1
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// _ <- e2
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// _ <- e3
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// _ <- e4
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// _ <- e5
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// _ <- e6
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// _ <- e7
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// _ <- e8
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// _ <- e8
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// _ <- e9
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// _ <- e10
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// _ <- e11
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// _ <- e12
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// _ <- e13
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// _ <- e14
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// _ <- e15
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// _ <- e16
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// _ <- e17
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// _ <- e18
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// _ <- e19
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// _ <- e20
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// _ <- e21
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// _ <- e22
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// _ <- e23
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// _ <- e24
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// _ <- e25
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// _ <- e26
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} yield ()
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}

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