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Yuki Okushi 2021-06-14 07:05:14 +09:00
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10
compiler/rustc_error_codes/src/error_codes/E0690.md
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@ -1,19 +1,19 @@
A struct with the representation hint `repr(transparent)` had zero or more than
one fields that were not guaranteed to be zero-sized.
A struct with the representation hint `repr(transparent)` had two or more fields
that were not guaranteed to be zero-sized.
Erroneous code example:
```compile_fail,E0690
#[repr(transparent)]
struct LengthWithUnit<U> { // error: transparent struct needs exactly one
struct LengthWithUnit<U> { // error: transparent struct needs at most one
value: f32, // non-zero-sized field, but has 2
unit: U,
}
```
Because transparent structs are represented exactly like one of their fields at
run time, said field must be uniquely determined. If there is no field, or if
there are multiple fields, it is not clear how the struct should be represented.
run time, said field must be uniquely determined. If there are multiple fields,
it is not clear how the struct should be represented.
Note that fields of zero-sized types (e.g., `PhantomData`) can also exist
alongside the field that contains the actual data, they do not count for this
error. When generic types are involved (as in the above example), an error is