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+# memoffset #
+
+[![](https://img.shields.io/crates/v/memoffset.svg)](https://crates.io/crates/memoffset)
+
+C-Like `offset_of` functionality for Rust structs.
+
+Introduces the following macros:
+ * `offset_of!` for obtaining the offset of a member of a struct.
+ * `offset_of_tuple!` for obtaining the offset of a member of a tuple. (Requires Rust 1.20+)
+ * `offset_of_union!` for obtaining the offset of a member of a union.
+ * `span_of!` for obtaining the range that a field, or fields, span.
+
+`memoffset` works under `no_std` environments.
+
+## Usage ##
+Add the following dependency to your `Cargo.toml`:
+
+```toml
+[dependencies]
+memoffset = "0.8"
+```
+
+These versions will compile fine with rustc versions greater or equal to 1.19.
+
+## Examples ##
+```rust
+use memoffset::{offset_of, span_of};
+
+#[repr(C, packed)]
+struct Foo {
+    a: u32,
+    b: u32,
+    c: [u8; 5],
+    d: u32,
+}
+
+fn main() {
+    assert_eq!(offset_of!(Foo, b), 4);
+    assert_eq!(offset_of!(Foo, d), 4+4+5);
+
+    assert_eq!(span_of!(Foo, a),        0..4);
+    assert_eq!(span_of!(Foo, a ..  c),  0..8);
+    assert_eq!(span_of!(Foo, a ..= c),  0..13);
+    assert_eq!(span_of!(Foo, ..= d),    0..17);
+    assert_eq!(span_of!(Foo, b ..),     4..17);
+}
+```
+
+## Usage in constants ##
+`memoffset` has support for compile-time `offset_of!` on rust>=1.65, or on older nightly compilers.
+
+### Usage on stable Rust ###
+Constant evaluation is automatically enabled and avilable on stable compilers starting with rustc 1.65.
+
+This is an incomplete implementation with one caveat:
+Due to dependence on [`#![feature(const_refs_to_cell)]`](https://github.com/rust-lang/rust/issues/80384), you cannot get the offset of a `Cell` field in a const-context.
+
+This means that if need to get the offset of a cell, you'll have to remain on nightly for now.
+
+### Usage on recent nightlies ###
+
+If you're using a new-enough nightly and you require the ability to get the offset of a `Cell`,
+you'll have to enable the `unstable_const` cargo feature, as well as enabling `const_refs_to_cell` in your crate root.
+
+Do note that `unstable_const` is an unstable feature that is set to be removed in a future version of `memoffset`.
+
+Cargo.toml:
+```toml
+[dependencies.memoffset]
+version = "0.8"
+features = ["unstable_const"]
+```
+
+Your crate root: (`lib.rs`/`main.rs`)
+```rust,ignore
+#![feature(const_refs_to_cell)]
+```
+
+### Usage on older nightlies ###
+In order to use it on an older nightly compiler, you must enable the `unstable_const` crate feature and several compiler features.
+
+Your crate root: (`lib.rs`/`main.rs`)
+```rust,ignore
+#![feature(const_ptr_offset_from, const_refs_to_cell)]
+```