Export concrete types (#22)

* Export concrete types

* Add zero value Cache test

README.md

@@ -26,8 +26,9 @@ import (
 )
 
 func main() {
-	// Create a new Cache instance with default configuration.
-	c := imcache.New[int32, string]()
+	// Zero value Cache is a valid non-sharded cache
+	// with no expiration, no sliding expiration and no eviction callback.
+	var c imcache.Cache[uint32, string]
 	// Set a new value with no expiration time.
 	c.Set(1, "one", imcache.WithNoExpiration())
 	// Get the value for the key 1.
@@ -55,12 +56,12 @@ c.Set(3, "three", imcache.WithExpiration(time.Second))
 If you want to use default expiration time for the given cache instance, you can use the `WithDefaultExpiration` `Expiration` option. By default the default expiration time is set to no expiration. You can set the default expiration time when creating a new `Cache` instance.
 
 ```go
-// Create a new Cache instance with default absolute expiration time equal to 1 second.
+// Create a new non-sharded cache instance with default absolute expiration time equal to 1 second.
 c1 := imcache.New(imcache.WithDefaultExpirationOption[int32, string](time.Second))
 // Set a new value with default expiration time (absolute).
 c1.Set(1, "one", imcache.WithDefaultExpiration())
 
-// Create a new Cache instance with default sliding expiration time equal to 1 second.
+// Create a new non-sharded cache instance with default sliding expiration time equal to 1 second.
 c2 := imcache.New(imcache.WithDefaultSlidingExpirationOption[int32, string](time.Second))
 // Set a new value with default expiration time (sliding).
 c2.Set(1, "one", imcache.WithDefaultExpiration())
@@ -73,13 +74,13 @@ c2.Set(1, "one", imcache.WithDefaultExpiration())
 It is possible to use the `Cleaner` to periodically remove expired entries from the cache. The `Cleaner` is a background goroutine that periodically removes expired entries from the cache. The `Cleaner` is disabled by default. You can enable it by calling the `StartCleaner` method. The `Cleaner` can be stopped by calling the `StopCleaner` method.
 
 ```go
-c := imcache.New[string, string]()
+var c imcache.Cache[string, string]
 // Start Cleaner which will remove expired entries every 5 minutes.
 _ = c.StartCleaner(5 * time.Minute)
 defer c.StopCleaner()
 ```
 
-To be notified when an entry is evicted from the cache, you can use the `EvictionCallback`. It's a function that accepts the key and value of the evicted entry along with the reason why the entry was evicted. `EvictionCallback` can be configured when creating a new `Cache` instance.
+To be notified when an entry is evicted from the cache, you can use the `EvictionCallback`. It's a function that accepts the key and value of the evicted entry along with the reason why the entry was evicted. `EvictionCallback` can be configured when creating a new `Cache` or `Sharded` instance.
 
 ```go
 package main
@@ -113,14 +114,14 @@ func main() {
 
 ### Sharding
 
-`imcache` supports sharding. It's possible to create a new `Cache` instance with a given number of shards. Each shard is a separate `Cache` instance. A shard for a given key is selected by computing the hash of the key and taking the modulus of the number of shards. `imcache` exposes the `Hasher64` interface that wraps `Sum64` accepting a key and returning a 64-bit hash of the input key. It can be used to implement custom sharding algorithms.
+`imcache` supports sharding. It's possible to create a new cache instance with a given number of shards. Each shard is a separate `Cache` instance. A shard for a given key is selected by computing the hash of the key and taking the modulus of the number of shards. `imcache` exposes the `Hasher64` interface that wraps `Sum64` accepting a key and returning a 64-bit hash of the input key. It can be used to implement custom sharding algorithms.
 
 Currently, `imcache` provides only one implementation of the `Hasher64` interface: `DefaultStringHasher64`. It uses the FNV-1a hash function.
 
-A sharded `Cache` instance can be created by calling the `NewSharded` method. It accepts the number of shards, `Hasher64` interface and optional configuration `Option`s as arguments.
+A `Sharded` instance can be created by calling the `NewSharded` method. It accepts the number of shards, `Hasher64` interface and optional configuration `Option`s as arguments.
 
 ```go
 c := imcache.NewSharded[string, string](4, imcache.DefaultStringHasher64{})
 ```
 
-All previous examples apply to sharded `Cache` instances as well.
+All previous examples apply to `Sharded` type as well.