_isOptional(type(of:)) Does Not Do What You Think It Does #28994
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In particular, if value is `Any` in a generic context, then `type(of: value)` is `Any.Protocol` which is never considered optional. As a result, the first clause here was never actually being used for `print()` or other similar paths. (Curiously, it _was_ used for string interpolation.) Fortunately? `print()` was producing the right results for optionals because of a dynamic cast bug that failed to unwrap optionals in these same contexts. <sigh>
tbkka
changed the title
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@swift-ci Please test Linux |
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@swift-ci Please smoke test |
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Looks good for preserving the existing behavior. (As we discussed previously, this still isn't sufficient if the value is a multiply-wrapped |
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The best technical answer is probably to eliminate the special case for Optional entirely. But that will require some additional discussion and socialization. |
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Yeah, ultimately it's only there in order to give Optional a fighting chance, because the dynamic casts that look for conformances below will look through Optionals. If we had separate "recursively unwrap and open an existential" and "test if this type conforms to a protocol" operations that didn't magically unwrap, we could do away with the special case. |
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In particular, if value is
Anyin a generic context, thentype(of: value)isAny.Protocolwhich is never considered optional. As a result, the first clause here (that provided special handling for printing optionals) was never actually being used forprint()or other similar paths. (Curiously, it was used for string interpolation.)Fortunately?
print()was producing the right results for optionals because of a dynamic cast bug that failed to unwrap optionals in these same contexts.Resolves rdar://58302667