grandpa-compatible digest items

substrate/core/sr-primitives/src/traits.rs

@@ -447,6 +447,10 @@ pub trait Block: Clone + Send + Sync + Codec + Eq + MaybeSerializeDebug + 'stati
 pub type HashFor<B> = <<B as Block>::Header as Header>::Hashing;
 /// Extract the number type for a block.
 pub type NumberFor<B> = <<B as Block>::Header as Header>::Number;
+/// Extract the digest type for a block.
+pub type DigestFor<B> = <<B as Block>::Header as Header>::Digest;
+/// Extract the digest item type for a block.
+pub type DigestItemFor<B> = <DigestFor<B> as Digest>::Item;
 
 /// A "checkable" piece of information, used by the standard Substrate Executive in order to
 /// check the validity of a piece of extrinsic information, usually by verifying the signature.