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#[cfg(maybe_uninit)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__let_base_ptr {
($name:ident, $type:ty) => {
let uninit = $crate::__priv::mem::MaybeUninit::<$type>::uninit();
let $name: *const $type = uninit.as_ptr();
};
}
#[cfg(not(maybe_uninit))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__let_base_ptr {
($name:ident, $type:ty) => {
let $name = $crate::__priv::mem::align_of::<$type>() as *const $type;
};
}
#[cfg(feature = "unstable_const")]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset_offset_from_unsafe {
($field:expr, $base:expr) => {{
let field = $field;
let base = $base;
unsafe { (field as *const u8).offset_from(base as *const u8) as usize }
}};
}
#[cfg(not(feature = "unstable_const"))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset_offset_from_unsafe {
($field:expr, $base:expr) => {
($field as usize) - ($base as usize)
};
}
#[macro_export(local_inner_macros)]
macro_rules! offset_of {
($parent:path, $field:tt) => {{
_memoffset__let_base_ptr!(base_ptr, $parent);
let field_ptr = raw_field!(base_ptr, $parent, $field);
_memoffset_offset_from_unsafe!(field_ptr, base_ptr)
}};
}
#[cfg(tuple_ty)]
#[macro_export(local_inner_macros)]
macro_rules! offset_of_tuple {
($parent:ty, $field:tt) => {{
_memoffset__let_base_ptr!(base_ptr, $parent);
let field_ptr = raw_field_tuple!(base_ptr, $parent, $field);
_memoffset_offset_from_unsafe!(field_ptr, base_ptr)
}};
}
#[cfg(test)]
mod tests {
#[test]
fn offset_simple() {
#[repr(C)]
struct Foo {
a: u32,
b: [u8; 2],
c: i64,
}
assert_eq!(offset_of!(Foo, a), 0);
assert_eq!(offset_of!(Foo, b), 4);
assert_eq!(offset_of!(Foo, c), 8);
}
#[test]
#[cfg_attr(miri, ignore)]
fn offset_simple_packed() {
#[repr(C, packed)]
struct Foo {
a: u32,
b: [u8; 2],
c: i64,
}
assert_eq!(offset_of!(Foo, a), 0);
assert_eq!(offset_of!(Foo, b), 4);
assert_eq!(offset_of!(Foo, c), 6);
}
#[test]
fn tuple_struct() {
#[repr(C)]
struct Tup(i32, i32);
assert_eq!(offset_of!(Tup, 0), 0);
assert_eq!(offset_of!(Tup, 1), 4);
}
#[test]
fn path() {
mod sub {
#[repr(C)]
pub struct Foo {
pub x: u32,
}
}
assert_eq!(offset_of!(sub::Foo, x), 0);
}
#[test]
fn inside_generic_method() {
struct Pair<T, U>(T, U);
fn foo<T, U>(_: Pair<T, U>) -> usize {
offset_of!(Pair<T, U>, 1)
}
assert_eq!(foo(Pair(0, 0)), 4);
}
#[cfg(tuple_ty)]
#[test]
fn test_tuple_offset() {
let f = (0i32, 0.0f32, 0u8);
let f_ptr = &f as *const _;
let f1_ptr = &f.1 as *const _;
assert_eq!(
f1_ptr as usize - f_ptr as usize,
offset_of_tuple!((i32, f32, u8), 1)
);
}
#[test]
fn test_raw_field() {
#[repr(C)]
struct Foo {
a: u32,
b: [u8; 2],
c: i64,
}
let f: Foo = Foo {
a: 0,
b: [0, 0],
c: 0,
};
let f_ptr = &f as *const _;
assert_eq!(f_ptr as usize + 0, raw_field!(f_ptr, Foo, a) as usize);
assert_eq!(f_ptr as usize + 4, raw_field!(f_ptr, Foo, b) as usize);
assert_eq!(f_ptr as usize + 8, raw_field!(f_ptr, Foo, c) as usize);
}
#[cfg(tuple_ty)]
#[test]
fn test_raw_field_tuple() {
let t = (0u32, 0u8, false);
let t_ptr = &t as *const _;
let t_addr = t_ptr as usize;
assert_eq!(
&t.0 as *const _ as usize - t_addr,
raw_field_tuple!(t_ptr, (u32, u8, bool), 0) as usize - t_addr
);
assert_eq!(
&t.1 as *const _ as usize - t_addr,
raw_field_tuple!(t_ptr, (u32, u8, bool), 1) as usize - t_addr
);
assert_eq!(
&t.2 as *const _ as usize - t_addr,
raw_field_tuple!(t_ptr, (u32, u8, bool), 2) as usize - t_addr
);
}
#[cfg(feature = "unstable_const")]
#[test]
fn const_offset() {
#[repr(C)]
struct Foo {
a: u32,
b: [u8; 2],
c: i64,
}
assert_eq!([0; offset_of!(Foo, b)].len(), 4);
}
#[cfg(feature = "unstable_const")]
#[test]
fn const_offset_interior_mutable() {
#[repr(C)]
struct Foo {
a: u32,
b: core::cell::Cell<u32>,
}
assert_eq!([0; offset_of!(Foo, b)].len(), 4);
}
#[cfg(feature = "unstable_const")]
#[test]
fn const_fn_offset() {
const fn test_fn() -> usize {
#[repr(C)]
struct Foo {
a: u32,
b: [u8; 2],
c: i64,
}
offset_of!(Foo, b)
}
assert_eq!([0; test_fn()].len(), 4);
}
}