Crate memoffset

A crate used for calculating offsets of struct members and their spans.

This functionality currently can not be used in compile time code such as const or const fn definitions.

Examples

use memoffset::{offset_of, span_of};

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

fn main() {
    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);
}

This functionality can be useful, for example, for checksum calculations:

#[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);

Macros

• offset_of
  Calculates the offset of the specified field from the start of the named struct.
• offset_of_tuple
  Calculates the offset of the specified field from the start of the tuple.
• offset_of_union
  Calculates the offset of the specified union member from the start of the union.
• raw_field
  Computes a const raw pointer to the given field of the given base pointer to the given parent type.
• raw_field_tuple
  Computes a const raw pointer to the given field of the given base pointer to the given parent tuple typle.
• raw_field_union
  Computes a const raw pointer to the given field of the given base pointer to the given parent tuple typle.
• span_of
  Produces a range instance representing the sub-slice containing the specified member.