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Type inference fails to find any common ancestor (higherKinds) #8882

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scabug opened this issue Oct 5, 2014 · 2 comments
Closed

Type inference fails to find any common ancestor (higherKinds) #8882

scabug opened this issue Oct 5, 2014 · 2 comments
Labels
infer lub tcpoly
Milestone
2.13.0-M5

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@scabug
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scabug commented Oct 5, 2014

The following code fails to compile due to what seems like incorrect type inference when two classes share a higher-kinded type ancestor.

import scala.language.higherKinds

class A[T[_]]
object B extends A[List]
object C extends A[Option]

// This compiles
val values = Seq[Any](B, C) 
// This doesn't
val values = Seq(B, C)

The error:

<console>:11: error: type mismatch;
 found   : B.type
 required: A[_ >: Option with List <: Product]
       val values = Seq(B, C)
                        ^
<console>:11: error: type mismatch;
 found   : C.type
 required: A[_ >: Option with List <: Product]
       val values = Seq(B, C)
                           ^

The expected behaviour, I would think, would be to infer the type of Any, as it would for Seq(B, 42).
@scabug
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scabug commented Oct 5, 2014

Imported From: https://issues.scala-lang.org/browse/SI-8882?orig=1
Reporter: Gal Topper (gtopper)
Affected Versions: 2.10.4, 2.11.0, 2.11.2
Duplicates #3528

@scabug
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scabug commented Oct 6, 2014

@retronym said:
I'm going to merge this with #3528. Thanks for the tiny minimization.

@joroKr21 joroKr21 mentioned this issue Feb 26, 2018
Merged
@scabug scabug mentioned this issue Mar 12, 2018
Open
joroKr21 added a commit to joroKr21/scala that referenced this issue Mar 14, 2018
@joroKr21
lub/glb for HKTs
9a2c195 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types. Improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
joroKr21 added a commit to joroKr21/scala that referenced this issue Apr 24, 2018
@joroKr21
lub/glb for HKTs
ceedc1b 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types. Improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
joroKr21 added a commit to joroKr21/scala that referenced this issue Apr 25, 2018
@joroKr21
lub/glb for HKTs
21399c8 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types. Improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
joroKr21 added a commit to joroKr21/scala that referenced this issue Apr 25, 2018
@joroKr21
lub/glb for HKTs
9a68913 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types. Improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
joroKr21 added a commit to joroKr21/scala that referenced this issue Apr 25, 2018
@joroKr21
lub/glb for HKTs
db56c19 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types. Improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
joroKr21 added a commit to joroKr21/scala that referenced this issue May 26, 2018
@joroKr21
lub/glb for HKTs
49feffe 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types. Improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
adriaanm pushed a commit to joroKr21/scala that referenced this issue Aug 3, 2018
@joroKr21 @adriaanm
lub/glb uses correct kind for higher-order type args
b6b0b03 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types when merging type constructor arguments
that are supplied for a type constructor parameter.

This improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
adriaanm pushed a commit to scala/scala that referenced this issue Aug 3, 2018
@joroKr21 @adriaanm
lub/glb uses correct kind for higher-order type args
25d14bf 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types when merging type constructor arguments
that are supplied for a type constructor parameter.

This improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
adriaanm pushed a commit to joroKr21/scala that referenced this issue Aug 6, 2018
@joroKr21 @adriaanm
lub/glb uses correct kind for higher-order type args
36ed6d4 
When computing the `lub/glb` of HKTs take care to produce
well-kinded types when merging type constructor arguments
that are supplied for a type constructor parameter.

This improves type inference.

A few tests with `-Xstrict-inference` were changed.
Other tests reveal a limitation of higher-kinded existentials.

Fixes scala/bug#8882 and promotes scala/bug#10700 to an error.
@SethTisue SethTisue added this to the 2.13.0-M5 milestone Aug 7, 2018
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