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