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/table/builder.rs

@@ -7,7 +7,7 @@ use std::sync::Arc;
 use anyhow::Result;
 
 use super::{BlockMeta, SsTable};
-use crate::{block::BlockBuilder, lsm_storage::BlockCache};
+use crate::{block::BlockBuilder, key::KeySlice, lsm_storage::BlockCache};
 
 /// Builds an SSTable from key-value pairs.
 pub struct SsTableBuilder {
@@ -29,7 +29,7 @@ impl SsTableBuilder {
     ///
     /// Note: You should split a new block when the current block is full.(`std::mem::replace` may
     /// be helpful here)
-    pub fn add(&mut self, key: &[u8], value: &[u8]) {
+    pub fn add(&mut self, key: KeySlice, value: &[u8]) {
         unimplemented!()
     }
 

mini-lsm-starter/src/table/iterator.rs

@@ -6,7 +6,7 @@ use std::sync::Arc;
 use anyhow::Result;
 
 use super::SsTable;
-use crate::{block::BlockIterator, iterators::StorageIterator};
+use crate::{block::BlockIterator, iterators::StorageIterator, key::KeySlice};
 
 /// An iterator over the contents of an SSTable.
 pub struct SsTableIterator {
@@ -27,21 +27,23 @@ impl SsTableIterator {
     }
 
     /// Create a new iterator and seek to the first key-value pair which >= `key`.
-    pub fn create_and_seek_to_key(table: Arc<SsTable>, key: &[u8]) -> Result<Self> {
+    pub fn create_and_seek_to_key(table: Arc<SsTable>, key: KeySlice) -> Result<Self> {
         unimplemented!()
     }
 
     /// Seek to the first key-value pair which >= `key`.
     /// Note: You probably want to review the handout for detailed explanation when implementing
     /// this function.
-    pub fn seek_to_key(&mut self, key: &[u8]) -> Result<()> {
+    pub fn seek_to_key(&mut self, key: KeySlice) -> Result<()> {
         unimplemented!()
     }
 }
 
 impl StorageIterator for SsTableIterator {
+    type KeyType<'a> = KeySlice<'a>;
+
     /// Return the `key` that's held by the underlying block iterator.
-    fn key(&self) -> &[u8] {
+    fn key(&self) -> KeySlice {
         unimplemented!()
     }