cache+neutrino: update existing Cache interface to use type parameters

[Roasbeef]

This change gives all LRU cache declaration a bit more context, and also added compile-time type safety. Users no longer need to cast items before inserting or retrieving from the cache. Along the way, we copied the list.List implementation from Go and updated that itself to be generic.

PR is best reviewed in order with each commit.

[Roasbeef]

cc @halseth

[Roasbeef]

Alternatively:

diff --git a/cache/lru/lru.go b/cache/lru/lru.go
index c08c825..bc3cb66 100644
--- a/cache/lru/lru.go
+++ b/cache/lru/lru.go
@@ -9,7 +9,7 @@ import (
 
 // elementMap is an alias for a map from a generic interface to a list.Element.
 type elementMap[K comparable, V any] struct {
-	m map[K]*Element[V]
+	m map[K]V
 }
 
 // Del deletes an item from the cache.
@@ -18,13 +18,13 @@ func (e *elementMap[K, V]) Del(key K) {
 }
 
 // Lookup attempts to lookup a value in the cache.
-func (e *elementMap[K, V]) Lookup(key K) (*Element[V], bool) {
+func (e *elementMap[K, V]) Lookup(key K) (V, bool) {
 	el, ok := e.m[key]
 	return el, ok
 }
 
 // Store attempts to store an item in the cache.
-func (e *elementMap[K, V]) Store(key K, val *Element[V]) {
+func (e *elementMap[K, V]) Store(key K, val V) {
 	e.m[key] = val
 }
 
@@ -51,7 +51,7 @@ type Cache[K comparable, V cache.Value] struct {
 
 	// cache is a generic cache which allows us to find an elements position
 	// in the ll list from a given key.
-	cache elementMap[K, entry[K, V]]
+	cache elementMap[K, *Element[entry[K, V]]]
 
 	// mtx is used to make sure the Cache is thread-safe.
 	mtx sync.RWMutex
@@ -63,7 +63,7 @@ func NewCache[K comparable, V cache.Value](capacity uint64) *Cache[K, V] {
 	return &Cache[K, V]{
 		capacity: capacity,
 		ll:       NewList[entry[K, V]](),
-		cache: elementMap[K, entry[K, V]]{
+		cache: elementMap[K, *Element[entry[K, V]]]{
 			m: make(map[K]*Element[entry[K, V]]),
 		},
 	}

Then elementMap can go back to being a typedef.

[guggero]

Very nice! Love the generic map as well, we'll likely use that in quite a few places. LGTM 🎉

The linter is failing but it looks like that's a general problem with the version we use (I can create a fix in another PR).

[Roasbeef]

The linter is failing but it looks like that's a general problem with the version we use (I can create a fix in another PR)

Seems like it can't handle the new generics syntax?

[halseth]

Very nice! 👯

Make a PR to go standard lib? 🤓