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Make clear that status quo ≠ guarantee

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Peter Todd 2019-05-18 22:27:33 -04:00
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commit a91ad60158
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1 changed files with 3 additions and 2 deletions
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src/test/run-pass/union/union-nonzero.rs
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@ -6,8 +6,9 @@
// For example, if a union `U` can contain both a `&T` and a `*const T`, there's definitely no // For example, if a union `U` can contain both a `&T` and a `*const T`, there's definitely no
// bit-value that an `Option<U>` could reuse as `None`; this test makes sure that isn't done. // bit-value that an `Option<U>` could reuse as `None`; this test makes sure that isn't done.
// //
// Secondly, this tests the status quo to not apply such optimizations to types containing unions // Secondly, this tests the status quo (not a guarantee; subject to change!) to not apply such
// even if they're theoretically possible. (discussion: https://github.com/rust-lang/rust/issues/36394) // optimizations to types containing unions even if they're theoretically possible. (discussion:
// https://github.com/rust-lang/rust/issues/36394)
// //
// Notably this nails down part of the behavior that `MaybeUninit` assumes: that a // Notably this nails down part of the behavior that `MaybeUninit` assumes: that a
// `Option<MaybeUninit<&u8>>` does not take advantage of non-zero optimization, and thus is a safe // `Option<MaybeUninit<&u8>>` does not take advantage of non-zero optimization, and thus is a safe