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