add key abstraction and prepare for MVCC (#28)

* add key abstraction and prepare for MVCC

Signed-off-by: Alex Chi <iskyzh@gmail.com>

* a little bit type exercise

Signed-off-by: Alex Chi <iskyzh@gmail.com>

* refactor tests

Signed-off-by: Alex Chi <iskyzh@gmail.com>

* fix clippy warnings

Signed-off-by: Alex Chi <iskyzh@gmail.com>

* refactor starter code

Signed-off-by: Alex Chi <iskyzh@gmail.com>

* final touch docs

Signed-off-by: Alex Chi <iskyzh@gmail.com>

---------

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/iterators/concat_iterator.rs

@@ -6,7 +6,10 @@ use std::sync::Arc;
 use anyhow::Result;
 
 use super::StorageIterator;
-use crate::table::{SsTable, SsTableIterator};
+use crate::{
+    key::KeySlice,
+    table::{SsTable, SsTableIterator},
+};
 
 /// Concat multiple iterators ordered in key order and their key ranges do not overlap. We do not want to create the
 /// iterators when initializing this iterator to reduce the overhead of seeking.
@@ -21,13 +24,15 @@ impl SstConcatIterator {
         unimplemented!()
     }
 
-    pub fn create_and_seek_to_key(sstables: Vec<Arc<SsTable>>, key: &[u8]) -> Result<Self> {
+    pub fn create_and_seek_to_key(sstables: Vec<Arc<SsTable>>, key: KeySlice) -> Result<Self> {
         unimplemented!()
     }
 }
 
 impl StorageIterator for SstConcatIterator {
-    fn key(&self) -> &[u8] {
+    type KeyType<'a> = KeySlice<'a>;
+
+    fn key(&self) -> KeySlice {
         unimplemented!()
     }
 

mini-lsm-starter/src/iterators/merge_iterator.rs

@@ -6,6 +6,8 @@ use std::collections::BinaryHeap;
 
 use anyhow::Result;
 
+use crate::key::KeySlice;
+
 use super::StorageIterator;
 
 struct HeapWrapper<I: StorageIterator>(pub usize, pub Box<I>);
@@ -21,7 +23,7 @@ impl<I: StorageIterator> Eq for HeapWrapper<I> {}
 impl<I: StorageIterator> PartialOrd for HeapWrapper<I> {
     #[allow(clippy::non_canonical_partial_ord_impl)]
     fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
-        match self.1.key().cmp(other.1.key()) {
+        match self.1.key().cmp(&other.1.key()) {
             cmp::Ordering::Greater => Some(cmp::Ordering::Greater),
             cmp::Ordering::Less => Some(cmp::Ordering::Less),
             cmp::Ordering::Equal => self.0.partial_cmp(&other.0),
@@ -49,8 +51,12 @@ impl<I: StorageIterator> MergeIterator<I> {
     }
 }
 
-impl<I: StorageIterator> StorageIterator for MergeIterator<I> {
-    fn key(&self) -> &[u8] {
+impl<I: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>> StorageIterator
+    for MergeIterator<I>
+{
+    type KeyType<'a> = KeySlice<'a>;
+
+    fn key(&self) -> KeySlice {
         unimplemented!()
     }
 

mini-lsm-starter/src/iterators/two_merge_iterator.rs

@@ -3,6 +3,8 @@
 
 use anyhow::Result;
 
+use crate::key::KeySlice;
+
 use super::StorageIterator;
 
 /// Merges two iterators of different types into one. If the two iterators have the same key, only
@@ -13,14 +15,24 @@ pub struct TwoMergeIterator<A: StorageIterator, B: StorageIterator> {
     // Add fields as need
 }
 
-impl<A: StorageIterator, B: StorageIterator> TwoMergeIterator<A, B> {
+impl<
+        A: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
+        B: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
+    > TwoMergeIterator<A, B>
+{
     pub fn create(a: A, b: B) -> Result<Self> {
         unimplemented!()
     }
 }
 
-impl<A: StorageIterator, B: StorageIterator> StorageIterator for TwoMergeIterator<A, B> {
-    fn key(&self) -> &[u8] {
+impl<
+        A: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
+        B: 'static + for<'a> StorageIterator<KeyType<'a> = KeySlice<'a>>,
+    > StorageIterator for TwoMergeIterator<A, B>
+{
+    type KeyType<'a> = KeySlice<'a>;
+
+    fn key(&self) -> KeySlice {
         unimplemented!()
     }