Inline assertions of the structural layout of a struct. This was implemented exclusively to make it easier to implement structs which conform to a specification which defines the start and end of a field. The specific use case was initially to help faithfully reproduce structures from the NVMe spec.
``` rust ust structuralassert::teststructure;
pub struct Foo { #[loc(0:0)] pub a: u8, #[loc(1:1)] pub b: u8, #[loc(2:3)] pub c: u16, #[loc(4:19)] pub d: u128, } ```