From 39a0df98f6ec82357b130d26433220ad7f13d7b0 Mon Sep 17 00:00:00 2001
From: Matt Baer <matt@baer.works>
Date: Sun, 11 Jun 2017 13:46:59 -0400
Subject: [PATCH] Add memoization module

---
 memo/memo.go | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 memo/memo.go

diff --git a/memo/memo.go b/memo/memo.go
new file mode 100644
index 0000000..8592b17
--- /dev/null
+++ b/memo/memo.go
@@ -0,0 +1,56 @@
+package memo
+
+import (
+	"sync"
+)
+
+type (
+	Memo struct {
+		f     Func
+		mu    sync.Mutex //guards cache
+		cache *entry
+	}
+
+	Func func() (interface{}, error)
+)
+
+type (
+	entry struct {
+		res   result
+		ready chan struct{} // close when res is read
+	}
+
+	result struct {
+		value interface{}
+		err   error
+	}
+)
+
+func New(f Func) *Memo {
+	return &Memo{
+		f: f,
+	}
+}
+
+func (memo *Memo) Invalidate() {
+	memo.mu.Lock()
+	memo.cache = nil
+	memo.mu.Unlock()
+}
+
+func (memo *Memo) Get() (value interface{}, err error) {
+	memo.mu.Lock()
+	if memo.cache == nil {
+		memo.cache = &entry{ready: make(chan struct{})}
+		memo.mu.Unlock()
+
+		memo.cache.res.value, memo.cache.res.err = memo.f()
+
+		close(memo.cache.ready)
+	} else {
+		memo.mu.Unlock()
+
+		<-memo.cache.ready
+	}
+	return memo.cache.res.value, memo.cache.res.err
+}