Merge #578: Implement Debug trait for Scalar type

8ed8cac Implement `Debug` trait for `Scalar` type. (Arik Sosman)

Pull request description:

  Currently, `Scalar` types do not implement the `Debug` trait, whereas most other types in the library do. Besides that being an upstream requirement for us, I believe it would also be quite useful for users of that type.

  Also implements the `Index` traits for `Scalar`.

ACKs for top commit:
  apoelstra:
    ACK 8ed8cac

Tree-SHA512: f254859144850e40badf6ace2b2a1b231e5ed224ec60861586cd5f2042167d89c759dc16a1075702bce90d810ac60db924ea8cb20d82099a42fddb2718da12db

src/scalar.rs

@@ -6,7 +6,7 @@
 //! provides the `Scalar` type and related.
 //!
 
-use core::fmt;
+use core::{fmt, ops};
 
 use crate::constants;
 
@@ -23,6 +23,7 @@ use crate::constants;
 #[allow(missing_debug_implementations)]
 #[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd)]
 pub struct Scalar([u8; 32]);
+impl_pretty_debug!(Scalar);
 
 const MAX_RAW: [u8; 32] = [
     0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFE,
@@ -107,6 +108,16 @@ impl Scalar {
     }
 }
 
+impl<I> ops::Index<I> for Scalar
+where
+    [u8]: ops::Index<I>,
+{
+    type Output = <[u8] as ops::Index<I>>::Output;
+
+    #[inline]
+    fn index(&self, index: I) -> &Self::Output { &self.0[index] }
+}
+
 impl From<crate::SecretKey> for Scalar {
     fn from(value: crate::SecretKey) -> Self { Scalar(value.secret_bytes()) }
 }