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Amend RFC 1758 (repr(transparent)) w.r.t. repr(align) #2271

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Jan 26, 2018
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Amend RFC 1758 (repr(transparent)) w.r.t. repr(align) #2271

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8 changes: 3 additions & 5 deletions text/1758-repr-transparent.md
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Expand Up @@ -117,16 +117,14 @@ have the same representation as their underlying types.

[RFC 1649]: https://github.com/rust-lang/rfcs/pull/1649

This new representation cannot be used with any other representation attribute
but alignment, to be able to specify a transparent wrapper with additional
alignment constraints:
This new representation cannot be used with any other representation attribute:

```rust
#[repr(transparent, align = "128")]
struct OverAligned(f64); // Behaves as a bare f64 with 128 bits alignment.
struct BogusAlign(f64); // Error, must be aligned like the underlying type.

#[repr(C, transparent)]
struct BogusRepr(f64); // Nonsensical, repr cannot be C and transparent.
struct BogusRepr(f64); // Error, repr cannot be C and transparent.
```

As a matter of optimisation, eligible `#[repr(Rust)]` structs behave as if
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