memoffset

https://docs.rs/memoffset/
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memoffset is a Rust crate used for calculating offsets of struct members and their spans.
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### Compile-fail example for _memoffset__field_check

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Doc example showing that _memoffset__field_check! prevents compilation when the field is accessed through a Deref impl. The example is marked compile_fail.

```rust
use memoffset::_memoffset__field_check;

struct Foo {
    foo: i32,
}

type BoxedFoo = Box<Foo>;

_memoffset__field_check!(BoxedFoo, foo);
```

--------------------------------

### Compile-fail example for _memoffset__field_check_tuple

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Doc example showing that _memoffset__field_check_tuple! prevents compilation when the type is not a tuple. The example is marked compile_fail.

```rust
use memoffset::_memoffset__field_check_tuple;

_memoffset__field_check_tuple!(i32, 0);
```

--------------------------------

### Compile-fail example for _memoffset__field_check_union

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Doc example showing that _memoffset__field_check_union! prevents compilation when the field is accessed through a Deref impl. The example is marked compile_fail.

```rust
use memoffset::_memoffset__field_check_union;

union Foo {
    variant_a: i32,
}

type BoxedFoo = Box<Foo>;

_memoffset__field_check_union!(BoxedFoo, variant_a);
```

--------------------------------

### Using offset_of! and span_of! macros

Source: https://docs.rs/memoffset/latest/src/memoffset/lib.rs.html

Shows how to use `offset_of!` and `span_of!` to get the offset and span of struct fields. The struct must be `#[repr(C, packed)]` for the offsets to be deterministic. The example asserts the offset of field `a` is 15 and its span is 15..19, and the span from `help_me_before_they_` to `a` is 0..15.

```rust
use memoffset::{offset_of, span_of};

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

assert_eq!(offset_of!(HelpMeIAmTrappedInAStructFactory, a), 15);
assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_ .. a), 0..15);
```

--------------------------------

### Public offset_of! macro with usage example

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines the public offset_of! macro that calculates the offset of a specified field from the start of a named struct. The example shows usage with a repr(C, packed) struct and asserts the offsets for fields a and b. Note that Rust's ABI is unstable and the offset value may change between compilations.

```rust
/// Calculates the offset of the specified field from the start of the named struct.
///
/// ## Examples
/// ```
/// use memoffset::offset_of;
///
/// #[repr(C, packed)]
/// struct Foo {
///     a: u32,
///     b: u64,
///     c: [u8; 5]
/// }
///
/// assert_eq!(offset_of!(Foo, a), 0);
/// assert_eq!(offset_of!(Foo, b), 4);
/// ```
///
/// ## Notes
/// Rust's ABI is unstable, and [type layout can be changed with each
/// compilation](https://doc.rust-lang.org/reference/type-layout.html).
///
/// Using `offset_of!` with a `repr(Rust)` struct will return the correct offset of the
/// specified `field` for a particular compilation, but the exact value may change
/// based on the compiler version, concrete struct type, time of day, or rustc's mood.
///
/// As a result, the value should not be retained and used between different compilations.
#[macro_export(local_inner_macros)]
macro_rules! offset_of {
```

--------------------------------

### offset_of usage example

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of.html

Demonstrates calculating field offsets for a packed C-representation struct.

```rust
use memoffset::offset_of;

#[repr(C, packed)]
struct Foo {
    a: u32,
    b: u64,
    c: [u8; 5]
}

assert_eq!(offset_of!(Foo, a), 0);
assert_eq!(offset_of!(Foo, b), 4);
```

--------------------------------

### offset_of_tuple usage example

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of_tuple.html

Shows how to use offset_of_tuple to get the offset of a field in a tuple. The assertion checks that the offset is non-negative, noting that tuples do not have a defined layout.

```rust
use memoffset::offset_of_tuple;

assert!(offset_of_tuple!((u8, u32), 1) >= 0, "Tuples do not have a defined layout");
```

--------------------------------

### span_of! range forms

Source: https://docs.rs/memoffset/latest/src/memoffset/span_of.rs.html

Examples of using range syntax to calculate spans between fields or spanning multiple fields.

```rust
        #[repr(C)]
        struct Florp {
            a: u32,
        }

        #[repr(C)]
        struct Blarg {
            x: u64,
            y: [u8; 56],
            z: Florp,
            egg: [[u8; 4]; 5],
        }

        // Love me some brute force
        assert_eq!(0..8, span_of!(Blarg, x));
        assert_eq!(64..68, span_of!(Blarg, z));
        assert_eq!(68..mem::size_of::<Blarg>(), span_of!(Blarg, egg));

        assert_eq!(8..64, span_of!(Blarg, y..z));
        assert_eq!(0..64, span_of!(Blarg, x..=y));
```

--------------------------------

### span_of! usage examples

Source: https://docs.rs/memoffset/latest/memoffset/macro.span_of.html

Examples of span_of! usage with a repr(C) struct. The assertions show the resulting ranges for various forms, including open-ended, exclusive, and inclusive ranges.

```rust
use memoffset::span_of;

#[repr(C)]
struct Florp {
    a: u32
}

#[repr(C)]
struct Blarg {
    x: [u32; 2],
    y: [u8; 56],
    z: Florp,
    egg: [[u8; 4]; 4]
}

assert_eq!(0..84,  span_of!(Blarg, ..));
assert_eq!(0..8,   span_of!(Blarg, .. y));
assert_eq!(0..64,  span_of!(Blarg, ..= y));
assert_eq!(0..8,   span_of!(Blarg, x));
assert_eq!(8..84,  span_of!(Blarg, y ..));
assert_eq!(0..8,   span_of!(Blarg, x .. y));
assert_eq!(0..64,  span_of!(Blarg, x ..= y));
```

--------------------------------

### Calculate union member offset

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of_union.html

Example demonstrating the use of offset_of_union to verify the offset of a field in a packed union.

```rust
use memoffset::offset_of_union;

#[repr(C, packed)]
union Foo {
    foo32: i32,
    foo64: i64,
}

assert!(offset_of_union!(Foo, foo64) == 0);
```

--------------------------------

### offset_of_tuple!

Source: https://docs.rs/memoffset/latest/index.html

Calculates the offset of the specified field from the start of the tuple.

```APIDOC
## offset_of_tuple!

### Description
Calculates the offset of the specified field from the start of the tuple.

### Usage
```rust
use memoffset::offset_of_tuple;

let tuple = (0u8, 1u16, 2u32);
let offset = offset_of_tuple!(tuple, 1);
```

### Parameters
- **TupleType** (type) - Required - The type of the tuple.
- **index** (usize) - Required - The index of the field whose offset is to be calculated.

### Returns
- **usize** - The offset in bytes from the start of the tuple to the specified field.
```

--------------------------------

### offset_of

Source: https://docs.rs/memoffset/latest/memoffset/index.html

Calculates the offset of the specified field from the start of the named struct.

```APIDOC
## offset_of

### Description
Calculates the offset of the specified field from the start of the named struct.

### Usage
Use the macro with the struct type and field name.

### Example
```rust
use memoffset::offset_of;

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

assert_eq!(offset_of!(HelpMeIAmTrappedInAStructFactory, a), 15);
```
```

--------------------------------

### offset_of!

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of.html

Calculates the offset of the specified field from the start of the named struct. The macro takes a parent type path and a field token, and returns the byte offset as a usize.

```APIDOC
## offset_of!

### Description
Calculates the offset of the specified field from the start of the named struct.

### Syntax
```rust
macro_rules! offset_of {
    ($parent:path, $field:tt) => { ... };
}
```

### Parameters
- `$parent` (path) - Required - The path to the struct type.
- `$field` (token) - Required - The name of the field whose offset is to be calculated.

### Return Value
Returns the byte offset of the field from the start of the struct, as a `usize`.

### Examples
```rust
use memoffset::offset_of;

#[repr(C, packed)]
struct Foo {
    a: u32,
    b: u64,
    c: [u8; 5]
}

assert_eq!(offset_of!(Foo, a), 0);
assert_eq!(offset_of!(Foo, b), 4);
```

### Notes
Rust's ABI is unstable, and type layout can be changed with each compilation. Using `offset_of!` with a `repr(Rust)` struct will return the correct offset of the specified `field` for a particular compilation, but the exact value may change based on the compiler version, concrete struct type, time of day, or rustc's mood. As a result, the value should not be retained and used between different compilations.
```

--------------------------------

### offset_of!

Source: https://docs.rs/memoffset/latest/index.html

Calculates the offset of the specified field from the start of the named struct.

```APIDOC
## offset_of!

### Description
Calculates the offset of the specified field from the start of the named struct.

### Usage
```rust
use memoffset::offset_of;

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

assert_eq!(offset_of!(HelpMeIAmTrappedInAStructFactory, a), 15);
```

### Parameters
- **StructType** (type) - Required - The name of the struct.
- **field** (field name) - Required - The field whose offset is to be calculated.

### Returns
- **usize** - The offset in bytes from the start of the struct to the specified field.
```

--------------------------------

### offset_of_tuple

Source: https://docs.rs/memoffset/latest/memoffset/index.html

Calculates the offset of the specified field from the start of the tuple.

```APIDOC
## offset_of_tuple

### Description
Calculates the offset of the specified field from the start of the tuple.

### Usage
Use the macro with the tuple type and field index.

### Example
```rust
use memoffset::offset_of_tuple;

let tuple = (0u8, 1u16, 2u32);
let offset = offset_of_tuple!(tuple, 1);
```
```

--------------------------------

### Internal macro _memoffset__offset_of_impl without stable_offset_of feature

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines a macro to implement the offset_of! macro when the stable_offset_of feature is not enabled. It creates a base pointer, gets the field pointer using raw_field!, and computes the offset using _memoffset_offset_from_unsafe.

```rust
#[cfg(not(stable_offset_of))]
#[macro_export(local_inner_macros)]
#[doc(hidden)]
macro_rules! _memoffset__offset_of_impl {
    ($parent:path, $field:tt) => {{
        // Get a base pointer (non-dangling if rustc supports `MaybeUninit`).
        _memoffset__let_base_ptr!(base_ptr, $parent);
        // Get field pointer.
        let field_ptr = raw_field!(base_ptr, $parent, $field);
        // Compute offset.
        _memoffset_offset_from_unsafe!(field_ptr, base_ptr)
    }};
}
```

--------------------------------

### offset_of_tuple!

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Calculates the offset of the specified field from the start of the tuple. Note that tuples do not have a defined layout, so the offset may be non-negative but not guaranteed to be zero.

```APIDOC
## offset_of_tuple!

### Description
Calculates the offset of the specified field from the start of the tuple.

### Syntax
`offset_of_tuple!($parent:ty, $field:tt)`

### Parameters
- `$parent` (ty) - Required - The tuple type.
- `$field` (tt) - Required - The field index (e.g., 0, 1, ...).

### Returns
The byte offset of the field from the start of the tuple.

### Example
```rust
use memoffset::offset_of_tuple;

assert!(offset_of_tuple!((u8, u32), 1) >= 0, "Tuples do not have a defined layout");
```
```

--------------------------------

### offset_of_union!

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of_union.html

Calculates the offset of the specified union member from the start of the union.

```APIDOC
## offset_of_union!

### Description
Calculates the offset of the specified union member from the start of the union.

### Syntax
```rust
macro_rules! offset_of_union {
    ($parent:path, $field:tt) => { ... };
}
```

### Parameters
- **$parent** (path) - Required - The union type.
- **$field** (token tree) - Required - The field name whose offset is to be calculated.

### Return Value
Returns the offset in bytes from the start of the union to the specified field.

### Example
```rust
use memoffset::offset_of_union;

#[repr(C, packed)]
union Foo {
    foo32: i32,
    foo64: i64,
}

assert!(offset_of_union!(Foo, foo64) == 0);
```

### Note
Due to `macro_rules!` limitations, this macro will accept structs with a single field as well as unions. This is not a stable guarantee, and future versions of this crate might fail on any use of this macro with a struct, without a semver bump.
```

--------------------------------

### offset_of_tuple

Source: https://docs.rs/memoffset/latest/memoffset

Calculates the offset of a specified field from the start of a tuple. Useful for tuple structures.

```APIDOC
## offset_of_tuple!

### Description
Calculates the offset of the specified field from the start of the tuple. This macro provides a way to obtain field offsets for tuples.

### Method
```rust
memoffset::offset_of_tuple!((u8, u32), 1)
```

```

--------------------------------

### offset_of_union

Source: https://docs.rs/memoffset/latest/memoffset/index.html

Calculates the offset of the specified union member from the start of the union.

```APIDOC
## offset_of_union

### Description
Calculates the offset of the specified union member from the start of the union.

### Usage
Use the macro with the union type and member name.

### Example
```rust
use memoffset::offset_of_union;

union MyUnion {
    a: u32,
    b: f32,
}

let offset = offset_of_union!(MyUnion, b);
```
```

--------------------------------

### offset_of_tuple macro definition

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of_tuple.html

Defines the offset_of_tuple macro that takes a tuple type and a field token, returning the offset of that field from the start of the tuple.

```rust
macro_rules! offset_of_tuple {
    ($parent:ty, $field:tt) => { ... };
}
```

--------------------------------

### Checksum calculation with span_of!

Source: https://docs.rs/memoffset/latest/src/memoffset/lib.rs.html

Illustrates using `span_of!` to compute a range for checksum calculation. The struct `Message` is `#[repr(C, packed)]` and the range from `header` to `checksum` is used to compute a CRC16 checksum. This example is marked `ignore` in the source, so it is not run as a test.

```rust
#[repr(C, packed)]
struct Message {
    header: MessageHeader,
    fragment_index: u32,
    fragment_count: u32,
    payload: [u8; 1024],
    checksum: u16
}

let checksum_range = &raw[span_of!(Message, header..checksum)];
let checksum = crc16(checksum_range);
```

--------------------------------

### offset_of_union

Source: https://docs.rs/memoffset/latest/memoffset

Calculates the offset of a specified union member from the start of the union. Works with union types.

```APIDOC
## offset_of_union!

### Description
Calculates the offset of the specified union member from the start of the union.

### Method
```rust
memoffset::offset_of_union!(MyUnion, field)
```

```

--------------------------------

### raw_field macro: compute const raw pointer to a struct field

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Defines the raw_field macro. It takes a base expression, a parent type path, and a field token. It first runs a field existence check to prevent deref coercion, then evaluates the base expression outside the unsafe block, and finally uses addr_of to get the field address. The base pointer must not be dangling but may point to uninitialized memory.

```rust
macro_rules! raw_field {
    ($base:expr, $parent:path, $field:tt) => {{
        _memoffset__field_check!($parent, $field);
        let base = $base; // evaluate $base outside the `unsafe` block

        // Get the field address.
        // Crucially, we know that this will not trigger a deref coercion because
        // of the field check we did above.
        #[allow(unused_unsafe)] // for when the macro is used in an unsafe block
        unsafe {
            _memoffset__addr_of!((*(base as *const $parent)).$field)
        }
    }};
}
```

--------------------------------

### span_of!(Struct, member_a .. member_b)

Source: https://docs.rs/memoffset/latest/memoffset/macro.span_of.html

Produces a sub-slice which starts at one field and ends at another. Supports exclusive, inclusive, and open-ended ranges.

```APIDOC
## span_of!(Struct, member_a .. member_b)

### Description
Produces a sub-slice which starts at one field and ends at another. Supports exclusive, inclusive, and open-ended ranges.

### Syntax
span_of!(Struct, member_a .. member_b) // Exclusive
span_of!(Struct, member_a ..= member_b) // Inclusive
span_of!(Struct, .. end) // Open-ended range (start to end)
span_of!(Struct, start ..) // Open-ended range (start to end)

### Parameters
- **Struct** (type path) - Required - The struct type to inspect.
- **member_a** (field identifier) - Required - The starting field.
- **member_b** (field identifier) - Required - The ending field.
- **end** (field identifier) - Required for open-ended ranges - The ending field.
- **start** (field identifier) - Required for open-ended ranges - The starting field.

### Safety
This form assumes that the first field is positioned before the second. This is only guaranteed for repr(C) structs. Usage with repr(Rust) structs may yield unexpected results.

### Example
```rust
use memoffset::span_of;

#[repr(C)]
struct Florp {
    a: u32
}

#[repr(C)]
struct Blarg {
    x: [u32; 2],
    y: [u8; 56],
    z: Florp,
    egg: [[u8; 4]; 4]
}

assert_eq!(0..84, span_of!(Blarg, ..));
assert_eq!(0..8, span_of!(Blarg, .. y));
assert_eq!(0..64, span_of!(Blarg, ..= y));
assert_eq!(8..84, span_of!(Blarg, y ..));
assert_eq!(0..8, span_of!(Blarg, x .. y));
assert_eq!(0..64, span_of!(Blarg, x ..= y));
```
```

--------------------------------

### Define _memoffset__addr_of macro with raw_ref_macros

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that uses addr_of! when raw_ref_macros is enabled. This is the first of two cfg variants for the same macro.

```rust
/// `addr_of!`, or just ref-then-cast when that is not available.
#[cfg(raw_ref_macros)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__addr_of {
    ($path:expr) => {{
        $crate::__priv::ptr::addr_of!($path)
    }};
}
```

--------------------------------

### Basic span_of! usage

Source: https://docs.rs/memoffset/latest/src/memoffset/span_of.rs.html

Demonstrates calculating the byte range of individual fields in a standard C-representation struct.

```rust
        #[repr(C)]
        struct Foo {
            a: u32,
            b: [u8; 2],
            c: i64,
        }

        assert_eq!(span_of!(Foo, a), 0..4);
        assert_eq!(span_of!(Foo, b), 4..6);
        assert_eq!(span_of!(Foo, c), 8..8 + 8);
```

--------------------------------

### Internal macro _memoffset__let_base_ptr with maybe_uninit feature

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines a macro to create a local base_ptr raw pointer of the given type, avoiding undefined behavior as much as possible when the maybe_uninit feature is enabled. It uses MaybeUninit to ensure the pointer does not dangle.

```rust
/// Macro to create a local `base_ptr` raw pointer of the given type, avoiding UB as
/// much as is possible currently.
#[cfg(maybe_uninit)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__let_base_ptr {
    ($name:ident, $type:ty) => {
        // No UB here, and the pointer does not dangle, either.
        // But we have to make sure that `uninit` lives long enough,
        // so it has to be in the same scope as `$name`. That's why
        // `let_base_ptr` declares a variable (several, actually)
        // instead of returning one.
        let uninit = $crate::__priv::mem::MaybeUninit::<$type>::uninit();
        let $name: *const $type = uninit.as_ptr();
    };
}
```

--------------------------------

### Define _memoffset__field_check macro with allow_clippy

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that checks field existence via a let pattern, with clippy allow attribute. This is the allow_clippy variant.

```rust
#[cfg(allow_clippy)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check {
    ($type:path, $field:tt) => {
        // Make sure the field actually exists. This line ensures that a
        // compile-time error is generated if $field is accessed through a
        // Deref impl.
        #[allow(clippy::unneeded_field_pattern)]
        let $type { $field: _, .. };
    };
}
```

--------------------------------

### Calculate constant offsets with interior mutability

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Demonstrates constant offset calculation for structs containing types with interior mutability.

```rust
    #[cfg(stable_offset_of)]
    #[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);
    }
```

--------------------------------

### Internal macro _memoffset__let_base_ptr without maybe_uninit feature

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines a macro to create a base pointer when the maybe_uninit feature is not enabled. It uses align_of to create a pointer, but notes that dereferencing it later is undefined behavior because the pointer is dangling.

```rust
#[cfg(not(maybe_uninit))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__let_base_ptr {
    ($name:ident, $type:ty) => {
        // No UB right here, but we will later dereference this pointer to
        // offset into a field, and that is UB because the pointer is dangling.
        let $name = $crate::__priv::mem::align_of::<$type>() as *const $type;
    };
}
```

--------------------------------

### Access raw union fields

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Demonstrates using raw_field_union! to calculate the address of union fields.

```rust
    #[test]
    fn test_raw_field_union() {
        #[repr(C)]
        union Foo {
            a: u32,
            b: [u8; 2],
            c: i64,
        }

        let f = Foo { a: 0 };
        let f_ptr = &f as *const _;
        assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, a) as usize);
        assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, b) as usize);
        assert_eq!(f_ptr as usize + 0, raw_field_union!(f_ptr, Foo, c) as usize);
    }
```

--------------------------------

### Define _memoffset__field_check_tuple macro with allow_clippy

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that checks the type argument is a tuple, with clippy allow attribute. This is the allow_clippy variant.

```rust
#[cfg(allow_clippy)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check_tuple {
    ($type:ty, $field:tt) => {
        // Make sure the type argument is a tuple
        #[allow(clippy::unneeded_wildcard_pattern)]
        let (_, ..): $type;
    };
}
```

--------------------------------

### Define _memoffset__field_check macro without allow_clippy

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that checks field existence via a let pattern, without clippy allow attribute. This is the non-allow_clippy variant.

```rust
#[cfg(not(allow_clippy))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check {
    ($type:path, $field:tt) => {
        // Make sure the field actually exists. This line ensures that a
        // compile-time error is generated if $field is accessed through a
        // Deref impl.
        let $type { $field: _, .. };
    };
}
```

--------------------------------

### Calculate constant offsets

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Shows that offset_of! can be used in constant contexts when supported by the compiler.

```rust
    #[cfg(any(stable_offset_of, stable_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);
    }
```

--------------------------------

### Define _memoffset__addr_of macro without raw_ref_macros

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Fallback macro that uses reference-then-cast, noting it is UB without addr_of!. This is the second cfg variant.

```rust
#[cfg(not(raw_ref_macros))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__addr_of {
    ($path:expr) => {{
        // This is UB because we create an intermediate reference to uninitialized memory.
        // Nothing we can do about that without `addr_of!` though.
        &$path as *const _
    }};
}
```

--------------------------------

### Calculate offset inside generic method

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Shows how to use offset_of! within a generic function context.

```rust
    #[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);
    }
```

--------------------------------

### Define _memoffset__field_check_union macro with allow_clippy

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that checks union field existence via an unsafe pattern, with clippy allow attributes. This is the allow_clippy variant.

```rust
#[cfg(allow_clippy)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check_union {
    ($type:path, $field:tt) => {
        // Make sure the field actually exists. This line ensures that a
        // compile-time error is generated if $field is accessed through a
        // Deref impl.
        #[allow(clippy::unneeded_wildcard_pattern)]
        // rustc1.19 requires unsafe here for the pattern; not needed in newer versions
        #[allow(unused_unsafe)]
        unsafe {
            let $type { $field: _ };
        }
    };
}
```

--------------------------------

### span_of! range forms

Source: https://docs.rs/memoffset/latest/memoffset/macro.span_of.html

Second form of span_of! returns a sub-slice that starts at one field and ends at another. Supports exclusive (..), inclusive (..=), and open-ended ranges. The inter-field form assumes the first field is positioned before the second; this is only guaranteed for repr(C) structs. Usage with repr(Rust) structs may yield unexpected results, such as downward-going ranges, spans that include unexpected fields, empty spans, or spans that include unexpected padding bytes.

```rust
// Exclusive
span_of!(Struct, member_a .. member_b)
// Inclusive
span_of!(Struct, member_a ..= member_b)

// Open-ended ranges
span_of!(Struct, .. end)
span_of!(Struct, start ..)
```

--------------------------------

### offset_of macro definition

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of.html

The signature of the offset_of macro.

```rust
macro_rules! offset_of {
    ($parent:path, $field:tt) => { ... };
}
```

--------------------------------

### Access raw struct fields

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Demonstrates using raw_field! to calculate the address of a struct field from a raw pointer.

```rust
    #[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);
    }
```

--------------------------------

### Define _memoffset__field_check_tuple macro without allow_clippy

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that checks the type argument is a tuple, without clippy allow attribute. This is the non-allow_clippy variant.

```rust
#[cfg(not(allow_clippy))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check_tuple {
    ($type:ty, $field:tt) => {
        // Make sure the type argument is a tuple
        let (_, ..): $type;
    };
}
```

--------------------------------

### span_of

Source: https://docs.rs/memoffset/latest/memoffset/index.html

Produces a range instance representing the sub-slice containing the specified member.

```APIDOC
## span_of

### Description
Produces a range instance representing the sub-slice containing the specified member.

### Usage
Use the macro with the struct type and field name or a range of fields.

### Example
```rust
use memoffset::span_of;

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_ .. a), 0..15);
```
```

--------------------------------

### Define _memoffset__field_check_union macro without allow_clippy

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Internal macro that checks union field existence via an unsafe pattern, without clippy allow attributes. This is the non-allow_clippy variant.

```rust
#[cfg(not(allow_clippy))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__field_check_union {
    ($type:path, $field:tt) => {
        // Make sure the field actually exists. This line ensures that a
        // compile-time error is generated if $field is accessed through a
        // Deref impl.
        #[allow(unused_unsafe)]
        unsafe {
            let $type { $field: _ };
        }
    };
}
```

--------------------------------

### span_of

Source: https://docs.rs/memoffset/latest/memoffset

Produces a range instance representing the sub-slice containing the specified member. It can also produce a range between two fields.

```APIDOC
## span_of!

### Description
Produces a range instance representing the sub-slice containing the specified member. It can be used to obtain byte ranges for a single field or a range of fields.

### Method
```rust
use memoffset::span_of;

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_..a), 0..15);
```

```

--------------------------------

### span_of!

Source: https://docs.rs/memoffset/latest/index.html

Produces a range instance representing the sub-slice containing the specified member.

```APIDOC
## span_of!

### Description
Produces a range instance representing the sub-slice containing the specified member.

### Usage
```rust
use memoffset::span_of;

#[repr(C, packed)]
struct HelpMeIAmTrappedInAStructFactory {
    help_me_before_they_: [u8; 15],
    a: u32
}

assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, a), 15..19);
assert_eq!(span_of!(HelpMeIAmTrappedInAStructFactory, help_me_before_they_ .. a), 0..15);
```

### Parameters
- **StructType** (type) - Required - The name of the struct.
- **field** (field name) - Required - The field or range of fields whose span is to be produced.

### Returns
- **Range** - A range instance representing the sub-slice containing the specified member.
```

--------------------------------

### offset_of_tuple!

Source: https://docs.rs/memoffset/latest/memoffset/macro.offset_of_tuple.html

Macro to calculate the offset of a field within a tuple.

```APIDOC
## Macro `offset_of_tuple!`

### Description
Calculates the offset of the specified field from the start of the tuple.

### Macro Definition
```rust
macro_rules! offset_of_tuple {
    ($parent:ty, $field:tt) => { ... };
}
```

### Parameters
- **$parent** (type) - Required - The tuple type whose field offset is to be calculated.
- **$field** (token) - Required - The index of the field within the tuple.

### Example
```rust
use memoffset::offset_of_tuple;

assert!(offset_of_tuple!((u8, u32), 1) >= 0, "Tuples do not have a defined layout");
```

```

--------------------------------

### Calculate offsets in constant functions

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Shows the use of offset_of! inside a const function.

```rust
    #[cfg(any(stable_offset_of, stable_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);
    }
```

--------------------------------

### raw_field!

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Macro to compute a const raw pointer to a field of a given base pointer and parent type.

```APIDOC
## raw_field!

### Description
Computes a const raw pointer to the given field of the given base pointer to the given parent type. The `base` pointer *must not* be dangling, but it *may* point to uninitialized memory.

### Syntax
```rust
raw_field!($base:expr, $parent:path, $field:tt)
```

### Parameters
- **$base** (expr) - Required - The base pointer expression. Must not be dangling, but may point to uninitialized memory.
- **$parent** (path) - Required - The parent type path.
- **$field** (tt) - Required - The field token tree.

### Return Value
A const raw pointer to the given field of the given base pointer.

### Notes
- The macro performs a compile-time field existence check.
- The field address is computed without triggering deref coercion.
- The macro is exported with `#[macro_export(local_inner_macros)]`.
```

--------------------------------

### Internal macro _memoffset__offset_of_impl with stable_offset_of feature

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines a macro to implement the offset_of! macro when the stable_offset_of feature is enabled. It delegates to the standard library's mem::offset_of! macro.

```rust
#[cfg(stable_offset_of)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset__offset_of_impl {
    ($parent:path, $field:tt) => {{
        $crate::__priv::mem::offset_of!($parent, $field)
    }};
}
```

--------------------------------

### Calculate struct field offset

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Demonstrates using offset_of! to find the byte offset of a field within a struct.

```rust
        pub struct Foo {
                pub x: u32,
            }
        }

        assert_eq!(offset_of!(sub::Foo, x), 0);
```

--------------------------------

### raw_field_tuple macro definition

Source: https://docs.rs/memoffset/latest/memoffset/macro.raw_field_tuple.html

The signature of the raw_field_tuple macro.

```rust
macro_rules! raw_field_tuple {
    ($base:expr, $parent:ty, $field:tt) => { ... };
}
```

--------------------------------

### span_of! with packed structs

Source: https://docs.rs/memoffset/latest/src/memoffset/span_of.rs.html

Shows how span_of! behaves with structs using #[repr(C, packed)], where field alignment is minimized.

```rust
        #[repr(C, packed)]
        struct Foo {
            a: u32,
            b: [u8; 2],
            c: i64,
        }

        assert_eq!(span_of!(Foo, a), 0..4);
        assert_eq!(span_of!(Foo, b), 4..6);
        assert_eq!(span_of!(Foo, c), 6..6 + 8);
```

--------------------------------

### span_of! complex range expressions

Source: https://docs.rs/memoffset/latest/src/memoffset/span_of.rs.html

Demonstrates advanced range usage including open-ended ranges and inclusive/exclusive boundaries.

```rust
        #[repr(C)]
        struct Member {
            foo: u32,
        }

        #[repr(C)]
        struct Test {
            x: u64,
            y: [u8; 56],
            z: Member,
            egg: [[u8; 4]; 4],
        }

        assert_eq!(span_of!(Test, ..x), 0..0);
        assert_eq!(span_of!(Test, ..=x), 0..8);
        assert_eq!(span_of!(Test, ..y), 0..8);
        assert_eq!(span_of!(Test, ..=y), 0..64);
        assert_eq!(span_of!(Test, ..z), 0..64);
        assert_eq!(span_of!(Test, ..=z), 0..68);
        assert_eq!(span_of!(Test, ..egg), 0..68);
        assert_eq!(span_of!(Test, ..=egg), 0..84);
        assert_eq!(span_of!(Test, ..), 0..mem::size_of::<Test>());
        assert_eq!(
            span_of!(Test, x..),
            offset_of!(Test, x)..mem::size_of::<Test>()
        );
        assert_eq!(
            span_of!(Test, y..),
            offset_of!(Test, y)..mem::size_of::<Test>()
        );

        assert_eq!(
            span_of!(Test, z..),
            offset_of!(Test, z)..mem::size_of::<Test>()
        );
        assert_eq!(
            span_of!(Test, egg..),
            offset_of!(Test, egg)..mem::size_of::<Test>()
        );
        assert_eq!(
            span_of!(Test, x..y),
            offset_of!(Test, x)..offset_of!(Test, y)
        );
        assert_eq!(
            span_of!(Test, x..=y),
            offset_of!(Test, x)..offset_of!(Test, y) + mem::size_of::<[u8; 56]>()
        );
```

--------------------------------

### Internal macro _memoffset_offset_from_unsafe without stable_const feature

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines a macro to compute the distance between two pointers when the stable_const feature is not enabled. It computes the offset by subtracting the base pointer address from the field pointer address.

```rust
#[cfg(not(stable_const))]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset_offset_from_unsafe {
    ($field:expr, $base:expr) => {
        // Compute offset.
        ($field as usize) - ($base as usize)
    };
}
```

--------------------------------

### raw_field_union!

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Macro to compute a const raw pointer to a field of a given base pointer and parent type, with a Deref-coercion check that supports unions.

```APIDOC
## raw_field_union!

### Description
Computes a const raw pointer to the given field of the given base pointer to the given parent tuple type. The `base` pointer *must not* be dangling, but it *may* point to uninitialized memory. This macro is the same as `raw_field`, except for a different Deref-coercion check that supports unions.

### Syntax
```rust
raw_field_union!($base:expr, $parent:path, $field:tt)
```

### Parameters
- **$base** (expr) - Required - The base pointer expression. Must not be dangling, but may point to uninitialized memory.
- **$parent** (path) - Required - The parent type path.
- **$field** (tt) - Required - The field token tree.

### Return Value
A const raw pointer to the given field of the given base pointer.

### Notes
- The macro performs a compile-time field existence check.
- The field address is computed without triggering deref coercion.
- The macro is exported with `#[macro_export(local_inner_macros)]`.
- Due to `macro_rules!` limitations, this check will accept structs with a single field as well as unions. This is not a stable guarantee, and future versions of this crate might fail on any use of this macro with a struct, without a semver bump.
```

--------------------------------

### raw_field_tuple

Source: https://docs.rs/memoffset/latest/memoffset/macro.raw_field_tuple.html

Documentation for the raw_field_tuple macro, which computes a const raw pointer to a field of a tuple type.

```APIDOC
## raw_field_tuple

### Description
Computes a const raw pointer to the given field of the given base pointer to the given parent tuple type. The `base` pointer must not be dangling, but it may point to uninitialized memory.

### Syntax
```rust
macro_rules! raw_field_tuple {
    ($base:expr, $parent:ty, $field:tt) => { ... };
}
```

### Parameters
- **$base** (expr) - Required - The base pointer expression. Must not be dangling, but may point to uninitialized memory.
- **$parent** (ty) - Required - The parent tuple type.
- **$field** (tt) - Required - The field token tree identifying the field within the tuple.

### Returns
A const raw pointer to the specified field of the parent tuple type.

### Usage
This macro is used to obtain a raw pointer to a field of a tuple type from a base pointer, without requiring the memory to be initialized.
```

--------------------------------

### raw_field_tuple!

Source: https://docs.rs/memoffset/latest/src/memoffset/raw_field.rs.html

Macro to compute a const raw pointer to a field of a given base pointer and parent tuple type.

```APIDOC
## raw_field_tuple!

### Description
Computes a const raw pointer to the given field of the given base pointer to the given parent tuple type. The `base` pointer *must not* be dangling, but it *may* point to uninitialized memory.

### Syntax
```rust
raw_field_tuple!($base:expr, $parent:ty, $field:tt)
```

### Parameters
- **$base** (expr) - Required - The base pointer expression. Must not be dangling, but may point to uninitialized memory.
- **$parent** (ty) - Required - The parent tuple type.
- **$field** (tt) - Required - The field token tree.

### Return Value
A const raw pointer to the given field of the given base pointer.

### Notes
- The macro performs a compile-time field existence check.
- The field address is computed without triggering deref coercion.
- The macro is exported with `#[macro_export(local_inner_macros)]`.
```

--------------------------------

### Internal macro _memoffset_offset_from_unsafe with stable_const feature

Source: https://docs.rs/memoffset/latest/src/memoffset/offset_of.rs.html

Defines a macro to compute the distance between two pointers when the stable_const feature is enabled. It evaluates the field and base expressions outside the unsafe block and uses offset_from for const-compatibility.

```rust
/// Macro to compute the distance between two pointers.
#[cfg(stable_const)]
#[macro_export]
#[doc(hidden)]
macro_rules! _memoffset_offset_from_unsafe {
    ($field:expr, $base:expr) => {{
        let field = $field; // evaluate $field outside the `unsafe` block
        let base = $base; // evaluate $base outside the `unsafe` block
        // Compute offset, with unstable `offset_from` for const-compatibility.
        // (Requires the pointers to not dangle, but we already need that for `raw_field!` anyway.)
        unsafe { (field as *const u8).offset_from(base as *const u8) as usize }
    }};
}
```
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