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unions and ABI and repr(C) #43

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Nov 15, 2018
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unions and ABI and repr(C) #43

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4 changes: 4 additions & 0 deletions reference/src/representation/unions.md
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Expand Up @@ -34,3 +34,7 @@ a field type to obtain a pointer to any field, and vice versa.
to keep the option of using non-zero offsets open for the future; whether this
is useful depends on what exactly the compiler-assumed invariants about union
contents are.

Even if the offsets happen to be all 0, there might still be differences in the
function call ABI. If you need to pass unions by-value across an FFI boundary,
you have to use `#[repr(C)]`.