Devin Coughlin b727b6d932 Treat potentially unavailable global variable references as optional. ...

This patch adds the ability (-enable-experimental-unavailable-as-optional) to
treat potentially unavailable declarations as if they had optional types. For
the moment, this is only implemented for global variables.

The high-level approach is to (1) record the potential unavailability of a
declaration reference in the overload choice during constraint generation; (2)
treat the declaration as if it had an optional type during overload resolution
(this is similar to how optional protocol members are treated); and (3) add an
implicit conversion (UnavailableToOptionalExpr) during constraint application
to represent the run-time availability check and optional injection.

This patch does not implement SILGen for UnavailableToOptionalExpr.


Swift SVN r22245

2014-09-24 00:07:46 +00:00

35 KiB

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