Module data 

AttachmentData<A> wrapper and field access.

This module encapsulates the fields of AttachmentData, ensuring they are only visible within this module. This visibility restriction guarantees the safety invariant: the vtable type must always match the actual attachment type.

Safety Invariant

Since AttachmentData can only be constructed via AttachmentData::new (which creates matching vtable and attachment), and fields cannot be modified after construction (no pub or pub(crate) fields), the types remain in sync throughout the value’s lifetime.

#[repr(C)] Layout

The #[repr(C)] attribute enables safe field projection even when the type parameter A is erased. This allows accessing the vtable field from a pointer to AttachmentData<Erased> without constructing an invalid reference to the full struct.

Structs

AttachmentData 🔒

Type-erased attachment data structure with vtable-based dispatch.