Update pattern spec for narrowed type of ITuple pattern #3891
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RikkiGibson
approved these changes
Sep 14, 2020
alrz
reviewed
Sep 15, 2020
proposals/csharp-9.0/patterns3.md
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| 6. If `P` is an `or` pattern, the *narrowed type* is the common type of the *narrowed type* of the subpatterns if such a common type exists. For this purpose, the common type algorithm considers only identity, boxing, and implicit reference conversions, and it considers all subpatterns of a sequence of `or` patterns (ignoring parenthesized patterns). | ||
| 7. If `P` is an `and` pattern, the *narrowed type* is the *narrowed type* of the right pattern. Moreover, the *narrowed type* of the left pattern is the *input type* of the right pattern. | ||
| 8. Otherwise the *narrowed type* of `P` is `P`'s input type. | ||
| 4. If `P` is [matched via the rules for](https://github.com/dotnet/csharplang/blob/master/proposals/csharp-8.0/patterns.md#positional-pattern) `ITuple`, the *narrowed type* is the type `System.ITuple`. |
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Event if the input type is not ITuple itself, rather a compatible one?
interface IMyTuple : ITuple { object Foo { get; } }
obj is IMyTuple and (1, 2) and { Foo: null } // Foo is not recognized?There was a problem hiding this comment.
Confirmed we indeed get an error. two first patterns should be swapped for this to work.
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Fixes dotnet/roslyn#44102