have hashdb be generic over DBValue

hashdb/Cargo.toml

@@ -6,8 +6,7 @@ description = "trait for hash-keyed databases."
 license = "GPL-3.0"
 
 [dependencies]
-elastic-array = { version = "0.10", optional = true }
 
 [features]
 default = ["std"]
-std = ["elastic-array"]
+std = []

hashdb/src/lib.rs

@@ -18,13 +18,10 @@
 
 #![cfg_attr(not(feature = "std"), no_std)]
 
-#[cfg(feature = "std")]
-extern crate elastic_array;
 #[cfg(feature = "std")]
 extern crate core;
 
 #[cfg(feature = "std")]
-use elastic_array::ElasticArray128;
 #[cfg(feature = "std")]
 use std::collections::HashMap;
 use core::{fmt::Debug, hash::Hash};
@@ -44,19 +41,15 @@ pub trait Hasher: Sync + Send {
 	fn hash(x: &[u8]) -> Self::Out;
 }
 
-/// `HashDB` value type.
-#[cfg(feature = "std")]
-pub type DBValue = ElasticArray128<u8>;
-
 /// Trait modelling datastore keyed by a hash defined by the `Hasher`.
 #[cfg(feature = "std")]
-pub trait HashDB<H: Hasher>: Send + Sync + AsHashDB<H> {
+pub trait HashDB<H: Hasher, T>: Send + Sync + AsHashDB<H, T> {
 	/// Get the keys in the database together with number of underlying references.
 	fn keys(&self) -> HashMap<H::Out, i32>;
 
 	/// Look up a given hash into the bytes that hash to it, returning None if the
 	/// hash is not known.
-	fn get(&self, key: &H::Out) -> Option<DBValue>;
+	fn get(&self, key: &H::Out) -> Option<&T>;
 
 	/// Check for the existance of a hash-key.
 	fn contains(&self, key: &H::Out) -> bool;
@@ -67,7 +60,7 @@ pub trait HashDB<H: Hasher>: Send + Sync + AsHashDB<H> {
 	fn insert(&mut self, value: &[u8]) -> H::Out;
 
 	/// Like `insert()`, except you provide the key and the data is all moved.
-	fn emplace(&mut self, key: H::Out, value: DBValue);
+	fn emplace(&mut self, key: H::Out, value: T);
 
 	/// Remove a datum previously inserted. Insertions can be "owed" such that the same number of `insert()`s may
 	/// happen without the data being eventually being inserted into the DB. It can be "owed" more than once.
@@ -76,18 +69,18 @@ pub trait HashDB<H: Hasher>: Send + Sync + AsHashDB<H> {
 
 /// Upcast trait.
 #[cfg(feature = "std")]
-pub trait AsHashDB<H: Hasher> {
+pub trait AsHashDB<H: Hasher, T> {
 	/// Perform upcast to HashDB for anything that derives from HashDB.
-	fn as_hashdb(&self) -> &HashDB<H>;
+	fn as_hashdb(&self) -> &HashDB<H, T>;
 	/// Perform mutable upcast to HashDB for anything that derives from HashDB.
-	fn as_hashdb_mut(&mut self) -> &mut HashDB<H>;
+	fn as_hashdb_mut(&mut self) -> &mut HashDB<H, T>;
 }
 
 // NOTE: There used to be a `impl<T> AsHashDB for T` but that does not work with generics. See https://stackoverflow.com/questions/48432842/implementing-a-trait-for-reference-and-non-reference-types-causes-conflicting-im
 // This means we need concrete impls of AsHashDB in several places, which somewhat defeats the point of the trait.
 #[cfg(feature = "std")]
-impl<'a, H: Hasher> AsHashDB<H> for &'a mut HashDB<H> {
-	fn as_hashdb(&self) -> &HashDB<H> { &**self }
-	fn as_hashdb_mut(&mut self) -> &mut HashDB<H> { &mut **self }
+impl<'a, H: Hasher, T> AsHashDB<H, T> for &'a mut HashDB<H, T> {
+	fn as_hashdb(&self) -> &HashDB<H, T> { &**self }
+	fn as_hashdb_mut(&mut self) -> &mut HashDB<H, T> { &mut **self }
 }