E0692 - Error codes index
Description: Book listing all Rust error codes

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# Error code E0692

A `repr(transparent)` type was also annotated with other, incompatible representation hints.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    #[repr(transparent, C)] // error: incompatible representation hints
    struct Grams(f32);
    }

A type annotated as `repr(transparent)` delegates all representation concerns to another type, so adding more representation hints is contradictory. Remove either the `transparent` hint or the other hints, like this:

    #![allow(unused)]
    fn main() {
    #[repr(transparent)]
    struct Grams(f32);
    }

Alternatively, move the other attributes to the contained type:

    #![allow(unused)]
    fn main() {
    #[repr(C)]
    struct Foo {
        x: i32,
        // ...
    }

    #[repr(transparent)]
    struct FooWrapper(Foo);
    }

Note that introducing another `struct` just to have a place for the other attributes may have unintended side effects on the representation:

    #![allow(unused)]
    fn main() {
    #[repr(transparent)]
    struct Grams(f32);

    #[repr(C)]
    struct Float(f32);

    #[repr(transparent)]
    struct Grams2(Float); // this is not equivalent to `Grams` above
    }

Here, `Grams2` is a not equivalent to `Grams` – the former transparently wraps a (non-transparent) struct containing a single float, while `Grams` is a transparent wrapper around a float. This can make a difference for the ABI.