From c2dc1e34d2cde4cbe19021e5c2ff45dccbbf1bd5 Mon Sep 17 00:00:00 2001
From: Josh Fyne <josh.fyne@gmail.com>
Date: Thu, 12 Jan 2023 09:26:39 +0000
Subject: [PATCH] feat: Adds a way to use generics with this library.

---
 memoize.go      | 38 +++++++++++++++++++++++++++
 memoize_test.go | 69 +++++++++++++++++++++++++++++++++++++++++++++++++
 readme.md       | 30 +++++++++++++++++++++
 3 files changed, 137 insertions(+)

diff --git a/memoize.go b/memoize.go
index 1ff6656..57d5cb7 100644
--- a/memoize.go
+++ b/memoize.go
@@ -1,6 +1,7 @@
 package memoize
 
 import (
+	"errors"
 	"time"
 
 	"github.com/patrickmn/go-cache"
@@ -47,3 +48,40 @@ func (m *Memoizer) Memoize(key string, fn func() (interface{}, error)) (interfac
 	})
 	return value, err, false
 }
+
+// ErrMismatchedType if data returned from the cache does not match the expected type.
+var ErrMismatchedType = errors.New("data returned does not match expected type")
+
+// MemoizedFunction the expensive function to be called.
+type MemoizedFunction[T any] func() (T, error)
+
+// Call executes and returns the results of the given function, unless there was a cached value of the same key.
+// Only one execution is in-flight for a given key at a time.
+// The boolean return value indicates whether v was previously stored.
+func Call[T any](m *Memoizer, key string, fn MemoizedFunction[T]) (T, error, bool) {
+	// Check cache
+	value, found := m.Storage.Get(key)
+	if found {
+		v, ok := value.(T)
+		if !ok {
+			return v, ErrMismatchedType, true
+		}
+		return v, nil, true
+	}
+
+	// Combine memoized function with a cache store
+	value, err, _ := m.group.Do(key, func() (any, error) {
+		data, innerErr := fn()
+
+		if innerErr == nil {
+			m.Storage.Set(key, data, cache.DefaultExpiration)
+		}
+
+		return data, innerErr
+	})
+	v, ok := value.(T)
+	if !ok {
+		return v, ErrMismatchedType, false
+	}
+	return v, err, false
+}
diff --git a/memoize_test.go b/memoize_test.go
index cf34c2e..81814b3 100644
--- a/memoize_test.go
+++ b/memoize_test.go
@@ -83,3 +83,72 @@ func (t *F) TestFailure() {
 	t.So(result.(int), ShouldEqual, 2)
 	t.So(cached, ShouldBeTrue)
 }
+
+// TestBasicGenerics adopts the code from readme.md into a simple test case
+// but using generics.
+func (t *F) TestBasicGenerics() {
+	expensiveCalls := 0
+
+	// Function tracks how many times its been called
+	expensive := func() (int, error) {
+		expensiveCalls++
+		return expensiveCalls, nil
+	}
+
+	cache := NewMemoizer(90*time.Second, 10*time.Minute)
+
+	// First call SHOULD NOT be cached
+	result, err, cached := Call(cache, "key1", expensive)
+	t.So(err, ShouldBeNil)
+	t.So(result, ShouldEqual, 1)
+	t.So(cached, ShouldBeFalse)
+
+	// Second call on same key SHOULD be cached
+	result, err, cached = Call(cache, "key1", expensive)
+	t.So(err, ShouldBeNil)
+	t.So(result, ShouldEqual, 1)
+	t.So(cached, ShouldBeTrue)
+
+	// First call on a new key SHOULD NOT be cached
+	result, err, cached = Call(cache, "key2", expensive)
+	t.So(err, ShouldBeNil)
+	t.So(result, ShouldEqual, 2)
+	t.So(cached, ShouldBeFalse)
+}
+
+// TestFailureGenerics checks that failed function values are not cached
+// when using generics.
+func (t *F) TestFailureGenerics() {
+	calls := 0
+
+	// This function will fail IFF it has not been called before.
+	twoForTheMoney := func() (int, error) {
+		calls++
+
+		if calls == 1 {
+			return calls, errors.New("Try again")
+		} else {
+			return calls, nil
+		}
+	}
+
+	cache := NewMemoizer(90*time.Second, 10*time.Minute)
+
+	// First call should fail, and not be cached
+	result, err, cached := Call(cache, "key1", twoForTheMoney)
+	t.So(err, ShouldNotBeNil)
+	t.So(result, ShouldEqual, 1)
+	t.So(cached, ShouldBeFalse)
+
+	// Second call should succeed, and not be cached
+	result, err, cached = Call(cache, "key1", twoForTheMoney)
+	t.So(err, ShouldBeNil)
+	t.So(result, ShouldEqual, 2)
+	t.So(cached, ShouldBeFalse)
+
+	// Third call should succeed, and be cached
+	result, err, cached = Call(cache, "key1", twoForTheMoney)
+	t.So(err, ShouldBeNil)
+	t.So(result, ShouldEqual, 2)
+	t.So(cached, ShouldBeTrue)
+}
diff --git a/readme.md b/readme.md
index a32d902..a7ec041 100644
--- a/readme.md
+++ b/readme.md
@@ -51,3 +51,33 @@ In the example above, `result` is:
 All the hard stuff is punted to patrickmn's [go-cache](https://github.com/patrickmn/go-cache) and the Go team's [x/sync/singleflight](https://github.com/golang/sync), I just lashed them together.
 
 Also note that `cache.Storage` is exported, so you can use the underlying cache features - such as [Flush](https://godoc.org/github.com/patrickmn/go-cache#Cache.Flush) or [SaveFile](https://godoc.org/github.com/patrickmn/go-cache#Cache.SaveFile).
+
+### Generics
+
+You can also use generics. The same example as above
+
+```golang
+import (
+	"time"
+
+	"github.com/kofalt/go-memoize"
+)
+
+// Any expensive call that you wish to cache
+expensive := func() (string, error) {
+	time.Sleep(3 * time.Second)
+	return "some data", nil
+}
+
+// Cache expensive calls in memory for 90 seconds, purging old entries every 10 minutes.
+cache := memoize.NewMemoizer(90*time.Second, 10*time.Minute)
+
+// This will call the expensive func, and return a string.
+result, err, cached := memoize.Call(cache, "key1", expensive)
+
+// This will be cached
+result, err, cached = memoize.Call(cache, "key1", expensive)
+
+// This uses a new cache key, so expensive is called again
+result, err, cached = memoize.Call(cache, "key2", expensive)
+```