improve bitfield type safety by allowing tuple struct field

user-defined tuple struct could be used to improve type safety.

TEST=cargo test
BUG=None

Change-Id: I8ce10fc51b79c277ab23029513b707f3dd621af5
Reviewed-on: https://chromium-review.googlesource.com/1546432
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: David Tolnay <dtolnay@chromium.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/bit_field/src/lib.rs b/bit_field/src/lib.rs
index 64a309b..bd11c3c 100644
--- a/bit_field/src/lib.rs
+++ b/bit_field/src/lib.rs
@@ -101,6 +101,30 @@
 //! }
 //! ```
 //!
+//! Fields may be user-defined single element tuple struct with primitive types. Use must specify
+//! the width with `#[bits = N]`. This should be used to improve type safety.
+//!
+//! ```
+//! extern crate bit_field;
+//!
+//! use bit_field::*;
+//!
+//! #[bitfield]
+//! #[bits = 60]
+//! struct AddressField(u64);
+//!
+//! impl AddressField {
+//!     pub fn new(addr: u64) -> AddressField {
+//!         AddressField(addr >> 4)
+//!     }
+//!
+//!     pub fn get_addr(&self) -> u64 {
+//!         self.0 << 4
+//!     }
+//! }
+//!
+//! ```
+//!
 //! Finally, fields may be of user-defined enum types. The enum must satisfy one of the following
 //! requirements.
 //!