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use ApproximatingTypeMap to simplify exhaustivity check code #4299

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Apr 13, 2018
Merged

use ApproximatingTypeMap to simplify exhaustivity check code #4299

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24 changes: 4 additions & 20 deletions compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -605,32 +605,16 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
*
*/
def instantiate(tp1: NamedType, tp2: Type)(implicit ctx: Context): Type = {
// expose abstract type references to their bounds or tvars according to variance
class AbstractTypeMap(maximize: Boolean)(implicit ctx: Context) extends TypeMap {
def expose(lo: Type, hi: Type): Type =
if (variance == 0)
newTypeVar(TypeBounds(lo, hi))
else if (variance == 1)
if (maximize) hi else lo
else
if (maximize) lo else hi
// expose type param references to their bounds according to variance
class AbstractTypeMap(maximize: Boolean)(implicit ctx: Context) extends ApproximatingTypeMap {
variance = if (maximize) 1 else -1

def apply(tp: Type): Type = tp match {
case tp: TypeRef if tp.underlying.isInstanceOf[TypeBounds] =>
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While you're at it, maybe replace this by tp.symbol.isTypeParam

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@allanrenucci : tp.symbol.isTypeParam will miss the case where the reference is a type member.

val lo = this(tp.info.loBound)
val hi = this(tp.info.hiBound)
// See tests/patmat/gadt.scala tests/patmat/exhausting.scala tests/patmat/t9657.scala
val exposed = expose(lo, hi)
debug.println(s"$tp exposed to =====> $exposed")
exposed

case AppliedType(tycon: TypeRef, args) if tycon.underlying.isInstanceOf[TypeBounds] =>
val args2 = args.map(this)
val lo = this(tycon.info.loBound).applyIfParameterized(args2)
val hi = this(tycon.info.hiBound).applyIfParameterized(args2)
val exposed = expose(lo, hi)
debug.println(s"$tp exposed to =====> $exposed")
exposed
range(lo, hi)

case _ =>
mapOver(tp)
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