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impl Not for ! by dtolnay · Pull Request #91122 · rust-lang/rust · GitHub

 3 months ago
source link: https://github.com/rust-lang/rust/pull/91122
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dtolnay commented on Nov 22, 2021

The lack of this impl caused trouble for me in some degenerate cases of macro-generated code of the form if !$cond {...}, even without feature(never_type) on a stable compiler. Namely if $cond contains a return or break or similar diverging expression, which would otherwise be perfectly legal in boolean position, the code previously failed to compile with:

error[E0600]: cannot apply unary operator `!` to type `!`
   --> library/core/tests/ops.rs:239:8
    |
239 |     if !return () {}
    |        ^^^^^^^^^^ cannot apply unary operator `!`

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