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@ -26,12 +26,11 @@ still consumes a byte of space.
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* DST pointers (fat pointers), tuples, and enums with fields are not a concept
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in C, and as such are never FFI-safe.
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* As an exception to the rule on enum with data, `Option<&T>` is
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FFI-safe if `*const T` is FFI-safe, and they have the same
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representation, using the null-pointer optimization: `Some<&T>` is
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represented as the pointer, and `None` is represented as a null
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pointer. (This rule applies to any enum defined the same way as
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libcore's `Option` type, and using the default repr.)
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* If `T` is an [FFI-safe non-nullable pointer
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type](ffi.html#the-nullable-pointer-optimization),
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`Option<T>` is guaranteed to have the same layout and ABI as `T` and is
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therefore also FFI-safe. As of this writing, this covers `&`, `&mut`,
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and function pointers, all of which can never be null.
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* Tuple structs are like structs with regards to `repr(C)`, as the only
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difference from a struct is that the fields aren’t named.
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