Fix variance handling for parameterized type aliases #8651
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
dwijnand
reviewed
Jan 21, 2020
The variance of a type alias was taken to be the variance of its right-hand side, but that doesn't make sense for a parameterized type alias which is free to appear in any position: variance checking should only kick in when it is applied to something. It was possible to work around this by using a type lambda instead of a type alias, cats just had to do that: typelevel/cats#3264
smarter
force-pushed
the
variance-alias
branch
from
e6b5ee7
to
b7d9d19
Compare
This comment has been minimized.
This comment has been minimized.
adriaanm
approved these changes
Jan 22, 2020
| override def variance = | ||
| // A non-applied parameterized type alias can appear in any variance position | ||
| if (typeParams.nonEmpty) | ||
| Invariant |
| else if (isLocalToThis) | ||
| Bivariant | ||
| else | ||
| info.typeSymbol.variance |
There was a problem hiding this comment.
I can no longer construct the soundness argument for this; but, then again, I also don't have a counter-example. (And it's been like this forever 🤷♂ )
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
This comment has been minimized.
|
green community build run: https://scala-ci.typesafe.com/job/scala-2.13.x-integrate-community-build/3148/ |
|
Yay |
SethTisue
changed the title
This was referenced Feb 11, 2020
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The variance of a type alias was taken to be the variance of its
right-hand side, but that doesn't make sense for a parameterized type
alias which is free to appear in any position: variance checking should
only kick in when it is applied to something.
It was possible to work around this by using a type lambda instead of a
type alias, cats just had to do that: typelevel/cats#3264