3 #![feature(const_raw_ptr_deref)]
4 #![feature(const_ptr_offset_from)]
16 pub const OFFSET: usize = {
17 let uninit = std::mem::MaybeUninit::<Struct>::uninit();
18 let base_ptr: *const Struct = &uninit as *const _ as *const Struct;
19 // The following statement is UB (taking the address of an uninitialized field).
20 // Const eval doesn't detect this right now, but it may stop compiling at some point
22 let field_ptr = unsafe { &(*base_ptr).field as *const () as *const u8 };
23 let offset = unsafe { field_ptr.offset_from(base_ptr as *const u8) };
27 pub const OFFSET_2: usize = {
28 let uninit = std::mem::MaybeUninit::<Struct2>::uninit();
29 let base_ptr: *const Struct2 = &uninit as *const _ as *const Struct2;
30 let field_ptr = unsafe { &(*base_ptr).field as *const u8 };
31 let offset = unsafe { field_ptr.offset_from(base_ptr as *const u8) };
35 pub const OVERFLOW: isize = {
36 let uninit = std::mem::MaybeUninit::<Struct2>::uninit();
37 let base_ptr: *const Struct2 = &uninit as *const _ as *const Struct2;
38 let field_ptr = unsafe { &(*base_ptr).field as *const u8 };
39 unsafe { (base_ptr as *const u8).offset_from(field_ptr) }
42 pub const OFFSET_EQUAL_INTS: isize = {
43 let ptr = 1 as *const u8;
44 unsafe { ptr.offset_from(ptr) }
48 assert_eq!(OFFSET, 0);
49 assert_eq!(OFFSET_2, 1);
50 assert_eq!(OVERFLOW, -1);
51 assert_eq!(OFFSET_EQUAL_INTS, 0);