Mark Lacey 186c2f251a [ConstraintSystem] Fix the ordering of functions with optional parameters. ...

Treat non-optional generic parameters as being more specialized than
optional generic parameters, and penalize any solutions that involve
generic arguments that are themselves Optional.

By doing these things, we can remove the special-cased code for the
two overloads of '??' in the stdlib, instead treating the (T?, T)
overload as better than the (T?, T?) overload except where a user
actually passes an optionally-typed value as the second parameter.

Fixes: rdar://problem/19748710

2018-07-18 11:43:44 -07:00

198 KiB

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