Add Checksum to [u8; 32] conversion

Author: chipshort

packages/std/src/checksum.rs

@@ -1,4 +1,5 @@
 use core::fmt;
+use core::ops::Deref;
 
 use schemars::JsonSchema;
 use serde::{de, ser, Deserialize, Deserializer, Serialize};
@@ -52,6 +53,25 @@ impl From<[u8; 32]> for Checksum {
     }
 }
 
+/// Just like Vec<u8>, Checksum is a smart pointer to [u8].
+/// This implements `*data` for us and allows us to
+/// do `&*data`, returning a `&[u8]` from a `&Checksum`.
+/// With [deref coercions](https://doc.rust-lang.org/1.22.1/book/first-edition/deref-coercions.html#deref-coercions),
+/// this allows us to use `&data` whenever a `&[u8]` is required.
+impl Deref for Checksum {
+    type Target = [u8; 32];
+
+    fn deref(&self) -> &Self::Target {
+        self.as_ref()
+    }
+}
+
+impl AsRef<[u8; 32]> for Checksum {
+    fn as_ref(&self) -> &[u8; 32] {
+        &self.0
+    }
+}
+
 /// Serializes as a hex string
 impl Serialize for Checksum {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
@@ -184,4 +204,18 @@ mod tests {
         let as_vec: Vec<u8> = checksum.into();
         assert_eq!(as_vec, checksum.0);
     }
+
+    #[test]
+    fn ref_conversions_work() {
+        let checksum = Checksum::generate(&[12u8; 17]);
+        // deref
+        let _: &[u8; 32] = &checksum;
+        let _: &[u8] = &*checksum;
+        // as_ref
+        let _: &[u8; 32] = checksum.as_ref();
+        let _: &[u8] = checksum.as_ref();
+        // as_slice
+        let _: &[u8; 32] = checksum.as_ref();
+        let _: &[u8] = checksum.as_ref();
+    }
 }