dotty.tools.dotc.core.TypeApplications
Reducer
Related Doc:
package TypeApplications
Can be overridden.
Can be overridden. By default, only the prefix is mapped.
Map this function over given type
Map this function over given type
A type map that tries to reduce (part of) the result type of the type lambda
tyconwith the givenargs(some of which are wildcard arguments represented by type bounds). Non-wildcard arguments are substituted everywhere as usual. A wildcard argument>: L <: His substituted for a type lambda parameterXonly under certain conditions.Xappears in a toplevel refinement of the form{ type A = X }
and there are no other occurrences of
Xin the reduced type. In that case the refinement above is replaced by{ type A >: L <: U }
The
allReplacedfield indicates whether all occurrences of type lambda parameters in the reduced type have been replaced with arguments.2. If Mode.AllowLambdaWildcardApply is not set: All refinements of the form
{ type A = X }
are replaced by:
{ type A >: L <: U }
Any other occurrence of
Xintyconis replaced byU, if the occurrence ofXintyconis covariant, or nonvariant, or byL, if the occurrence is contravariant.The idea is that the
AllowLambdaWildcardApplymode is used to check whether a type can be soundly reduced, and to give an error or warning if that is not the case. By contrast, the default mode, withAllowLambdaWildcardApplynot set, reduces all applications even if this yields a different type, so its postcondition is that no type parameters oftyconappear in the result type. Using this mode, we can guarantee thatappliedTowill never produce a higher-kinded application with a type lambda as type constructor.