Implement 'join' for optional types and a special case for 'nil'. #4408
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@swift-ci please test macOS |
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| //===--- TypeJoinMeet.cpp - Swift Type "Join" and "Meet" -----------------===// | |||
| //===--- TypeJoinjoin.cpp - Swift Type "Join" and "join" -----------------===// | |||
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Doug is hereby enmeeted from using sed again.
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Drat! Will fix. |
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I'm not a type checker expert but everything else looks good. |
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This isn't specifically addressing any regression that I know of (I originally thought it did), so probably not for 3.0. Whaddya think, @rudkx ? |
…e for 'nil'. The join operation for optional types is straightforward to define/implement: join(T?, U) ::= join(T, U)? join(T, U?) ::= join(T, U)? join(T?, U?) ::= join(T, U)? As a special case in the constraint solver, handle the join of a 'nil' literal with a non-ExpressibleByNilLiteral-conforming concrete type 'T' to produce 'T?'. This allows us, e.g., infer [String?] for the expressions ["hello", nil] and true ? "hello" nil for example. Fixes rdar://problem/16326914.
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Force-merging; the CI shouldn't pay for my comment fixes. |
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@DougGregor Yeah, I don't think we need to take this now. |
kateinoigakukun
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Handle `swift_once` workaround in a proper way
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What's in this pull request?
The join operation for optional types is straightforward to define/implement:
As a special case in the constraint solver, handle the join of a 'nil'
literal with a non-ExpressibleByNilLiteral-conforming concrete type
'T' to produce 'T?'. This allows us, e.g., infer [String?] for the
expressions
and
for example.
Resolved bug number: (rdar://problem/16326914)
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