Thinking about indexes

storage_engine/src/index.rs

@@ -4,13 +4,14 @@ use tokio::fs::{File, OpenOptions, DirBuilder};
 use std::path::Path;
 
 use std::collections::{BTreeMap};
+use async_trait::async_trait;
 
 use bincode;
 use bincode::{Decode, Encode};
 use crate::binary_coding::{encode, decode, encode_sequence, decode_sequence};
 use tokio::fs;
 
-use crate::error::{Error, DecodeErrorKind};
+use crate::error::Error;
 
 use std::mem::size_of;
 
@@ -19,6 +20,7 @@ type Result<T> = std::result::Result<T, Error>;
 // Implements a persistant self-balancing Binary Search Tree. Nope.
 // We need fixed-size nodes. But we want to index Strings which are variable length.
 
+#[derive(Debug)]
 pub struct Index<K, V> {
     file: File,
     // None means index is asleep on disk.
@@ -28,11 +30,28 @@ pub struct Index<K, V> {
     value_type: PhantomData<V>,
 }
 
+#[derive(Debug)]
 pub struct IndexHeader {
 }
 
+use crate::storage_engine::FilePosition;
+
+#[async_trait]
+pub trait SomethingSupportingLeq {
+    async fn less_than_eq(&mut self, file_position0: FilePosition, file_position1: FilePosition) -> std::result::Result<bool, Error>;
+}
+
 impl <K, V>Index<K, V> {
-    pub async fn new(file_name: &str) -> Result<Index<K, V>> {
+    // TODO: delete
+    // pub async fn new<F, Fut, Store>(file_name: &str, less_than_eq: &F) -> Result<Index<K, V>> 
+    //     where F: Fn(&mut Store, K, K) -> Fut,
+    //           Store: SomethingSupportingLeq,
+    //           Fut: Future<Output=std::result::Result<bool, Error>>,
+    // {
+    //     todo!()
+    // }
+    pub async fn new(file_name: &str) -> Result<Index<K, V>> 
+    {
         todo!()
     }
 
@@ -56,9 +75,11 @@ impl <K, V>Index<K, V> {
         todo!()
     }
 
-    pub async fn lookup(&mut self, k: K) -> Result<Option<V>> 
+    pub async fn lookup<Store>(&mut self, store: &mut Store, k: K) -> Result<Option<V>> 
         where K: Encode + Decode,
+              Store: SomethingSupportingLeq,
     {
+        let x = store.less_than_eq(123, 123).await?;
         todo!()
     }