Document which union patterns are unsafe - #2350
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I think this kind of definition of what patterns "access" a thing could also be useful for implementing a lint for rust-lang/rust#158387 (comment). cc @Nadrieril |
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| - [Reference patterns](../patterns.md#reference-patterns) | ||
| - [Non-reference patterns](../patterns.md#r-patterns.ident.binding.non-reference) matching reference values | ||
| - [Struct](../patterns.md#struct-patterns) and [tuple struct](../patterns.md#tuple-struct-patterns) patterns which correspond to an enum variant | ||
| - [Path patterns](../patterns.md#path-patterns), if the result of expanding the constant into a pattern contains one of the above, or if the expanded pattern could not have been written directly at the location where it is used due to field privacy or `#[non_exhaustive]`. |
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I'd like to add constant patterns there, because it should be allowed to turn a constant patter nmatch into a call to PartialEq::eq for performance. This conflicts with https://doc.rust-lang.org/reference/patterns.html?highlight=patterns#r-patterns.const.translation a bit so we conceptually are saying "unsafety checking is done before we expand constant patterns"
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Documents rust-lang/rust#161771.