Implement DerefMut for User and Admin

As we want to change some methods to take a mutable reference to a
Device, we implement DerefMut for User<T> and Admin<T> so that users can
obtain a mutable reference to the wrapped device.

2 files changed, 17 insertions, 3 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index a9e3065..fcba0f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,8 @@ SPDX-License-Identifier: MIT
 - Always return a `Result` in functions that communicate with a device.
 - Combine `get_{major,minor}_firmware_version` into `get_firmware_version`.
 - Add `set_encrypted_volume_mode` to `Storage`.
+- Use mutability to represent changes to the device status:
+  - Implement `DerefMut` for `User<T>` and `Admin<T>`.
 
 # v0.3.4 (2019-01-20)
 - Fix authentication methods that assumed that `char` is signed.
diff --git a/src/auth.rs b/src/auth.rs
index 8978f32..8cec49c 100644
--- a/src/auth.rs
+++ b/src/auth.rs
@@ -1,7 +1,7 @@
 // Copyright (C) 2018-2019 Robin Krahl <robin.krahl@ireas.org>
 // SPDX-License-Identifier: MIT
 
-use std::ops::Deref;
+use std::ops;
 use std::os::raw::c_char;
 use std::os::raw::c_int;
 
@@ -211,7 +211,7 @@ impl<T: Device> User<T> {
     }
 }
 
-impl<T: Device> Deref for User<T> {
+impl<T: Device> ops::Deref for User<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -219,6 +219,12 @@ impl<T: Device> Deref for User<T> {
     }
 }
 
+impl<T: Device> ops::DerefMut for User<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.device
+    }
+}
+
 impl<T: Device> GenerateOtp for User<T> {
     fn get_hotp_code(&self, slot: u8) -> Result<String, Error> {
         result_from_string(unsafe {
@@ -246,7 +252,7 @@ impl<T: Device> AuthenticatedDevice<T> for User<T> {
     }
 }
 
-impl<T: Device> Deref for Admin<T> {
+impl<T: Device> ops::Deref for Admin<T> {
     type Target = T;
 
     fn deref(&self) -> &Self::Target {
@@ -254,6 +260,12 @@ impl<T: Device> Deref for Admin<T> {
     }
 }
 
+impl<T: Device> ops::DerefMut for Admin<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.device
+    }
+}
+
 impl<T: Device> Admin<T> {
     /// Forgets the user authentication and returns an unauthenticated device.  This method
     /// consumes the authenticated device.  It does not perform any actual commands on the