New design based on *mut T

src/access.rs

@@ -1,3 +1,6 @@
+
+pub trait Access {}
+
 /// Helper trait that is implemented by [`ReadWrite`] and [`ReadOnly`].
 pub trait Readable {}
 
@@ -7,16 +10,20 @@ pub trait Writable {}
 /// Zero-sized marker type for allowing both read and write access.
 #[derive(Debug, Copy, Clone)]
 pub struct ReadWrite;
+impl Access for ReadWrite {}
 impl Readable for ReadWrite {}
 impl Writable for ReadWrite {}
 
 /// Zero-sized marker type for allowing only read access.
 #[derive(Debug, Copy, Clone)]
 pub struct ReadOnly;
 
+impl Access for ReadOnly {}
 impl Readable for ReadOnly {}
 
 /// Zero-sized marker type for allowing only write access.
 #[derive(Debug, Copy, Clone)]
 pub struct WriteOnly;
+
+impl Access for WriteOnly {}
 impl Writable for WriteOnly {}