Trait HasField

Source

#[doc(hidden)] pub unsafe trait HasField<Field, const VARIANT_ID: i128, const FIELD_ID: i128> {
    type Type: ?Sized;

    // Required methods
    fn only_derive_is_allowed_to_implement_this_trait()
       where Self: Sized;
    fn project(slf: PtrInner<'_, Self>) -> *mut Self::Type;
}

Expand description

Projects a given field from Self.

All implementations of HasField for a particular field f in Self should use the same Field type; this ensures that Field is inferable given an explicit VARIANT_ID and FIELD_ID.

§Safety

A field f is HasField for Self if and only if:

If Self is a struct or union type, then VARIANT_ID is STRUCT_VARIANT_ID or UNION_VARIANT_ID respectively; otherwise, if Self is an enum type, VARIANT_ID is the numerical index of the enum variant in which f appears.
If f has name n, FIELD_ID is zerocopy::ident_id!(n); otherwise, if f is at index i, FIELD_ID is zerocopy::ident_id!(i).
Field is a type with the same visibility as f.
Type has the same type as f.

The caller must not assume that a pointer’s referent being aligned implies that calling project on that pointer will result in a pointer to an aligned referent. For example, HasField may be implemented for #[repr(packed)] structs.

The implementation of project must satisfy its safety post-condition.