diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/dotty/tools/dotc/core/ConstraintHandling.scala | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/src/dotty/tools/dotc/core/ConstraintHandling.scala b/src/dotty/tools/dotc/core/ConstraintHandling.scala index 95fa40704..0e155b9e1 100644 --- a/src/dotty/tools/dotc/core/ConstraintHandling.scala +++ b/src/dotty/tools/dotc/core/ConstraintHandling.scala @@ -177,7 +177,25 @@ trait ConstraintHandling { case tp: RefinedType if param occursIn tp.refinedInfo => tp.parent case tp: WildcardType => val bounds = tp.optBounds.orElse(TypeBounds.empty).bounds - if (fromBelow == (variance >= 0)) bounds.lo else bounds.hi + // Try to instantiate the wildcard to a type that is known to conform to it. + // This means: + // If fromBelow is true, we minimize the type overall + // Hence, if variance < 0, pick the maximal safe type: bounds.lo + // (i.e. the whole bounds range is over the type) + // if variance > 0, pick the minimal safe type: bounds.hi + // (i.e. the whole bounds range is under the type) + // if variance == 0, pick bounds.lo anyway (this is arbitrary but in line with + // the principle that we pick the smaller type when in doubt). + // If fromBelow is false, we maximize the type overall and reverse the bounds + // if variance != 0. For variance == 0, we still minimize. + // In summary we pick the bound given by this table: + // + // variance | -1 0 1 + // ------------------------ + // from below | lo lo hi + // from above | hi lo lo + // + if (variance == 0 || fromBelow == (variance < 0)) bounds.lo else bounds.hi case _ => tp } } |