From the Swift documentation:
"If you define an optional variable without providing a default value,
the variable is automatically set to nil for you."
As of now:
* old APIs are just marked as `deprecated` not `unavaiable`. To make it
easier to co-operate with other toolchain repos.
* Value variant of API is implemented as public @private
`_ofInstance(_:)`.
These provide the same functionality as the one-argument versions for both
2 and 3 argument closures. Since these are less common, the same thing can be
achieved by composing the one-argument version. rdar://problem/26529498
All generic bridgeable types can bridge for all their instantiations now. Removing this ferrets out some now-unnecessary traps that check for unbridgeable parameter types.
Foundation provides a number of specific operators defined in the
global scope. Push all of these into their corresponding types. This
cleanup helps verify that the SE-0091 implementation is generally
functional.
