Handle nullability info in by-name arguments #7727
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abeln approved these changes Dec 13, 2019
Implements the scheme described in my comment to scala#7546. - We type check an argument without or with flow info, depending on whether the function part of the application is known to take a call-by-name parameter. If we know nothing about the function part, we assume call-by-value. - At the end of type checking an application, if the argument is known to be by-name, remove all x.$asInstanceOf$[T] casts in the argument where x is a mutable variable, and run the type assigner (not the type checker!) again on the result. If this succeeds and gives a type that is still compatible with the formal parameter type, we are done. - Otherwise, issue an error saying that the argument cannot be treated as call-by-name since it contains flow-assumptions about mutable variables. As a remedy, suggest to wrap the argument in a `scala.compiletime.byName(...)` call. Here, `byName` is defined as follws: ``` inline def byName[T](x: => T): T ``` Wrapping an argument with byName means that we know statically that it is passed to a by-name parameter, so it will be typechecked without flow info.
odersky force-pushed the change-byname-nullable branch from a0e3525 to df71c9a Compare Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
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Implements the scheme described in my comment to #7546.
depending on whether the function part of the application
is known to take a call-by-name parameter. If we know nothing
about the function part, we assume call-by-value.
known to be by-name, remove all x.$asInstanceOf$[T] casts in the
argument where x is a mutable variable, and run the (re-)typer again
on the result. If this succeeds and gives a type that is still compatible
with the formal parameter type, we are done.
as call-by-name since it contains flow-assumptions about mutable variables.
As a remedy, suggest to wrap the argument in a
scala.compiletime.byName(...)call. Here,
byNameis defined as follws:it is passed to a by-name parameter, so it will be typechecked without
flow info.