good good study, day day up!

vendor/gopl.io/ch9/memo1/memo.go

@@ -0,0 +1,40 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 272.
+
+//!+
+
+// Package memo provides a concurrency-unsafe
+// memoization of a function of type Func.
+package memo
+
+// A Memo caches the results of calling a Func.
+type Memo struct {
+	f     Func
+	cache map[string]result
+}
+
+// Func is the type of the function to memoize.
+type Func func(key string) (interface{}, error)
+
+type result struct {
+	value interface{}
+	err   error
+}
+
+func New(f Func) *Memo {
+	return &Memo{f: f, cache: make(map[string]result)}
+}
+
+// NOTE: not concurrency-safe!
+func (memo *Memo) Get(key string) (interface{}, error) {
+	res, ok := memo.cache[key]
+	if !ok {
+		res.value, res.err = memo.f(key)
+		memo.cache[key] = res
+	}
+	return res.value, res.err
+}
+
+//!-

vendor/gopl.io/ch9/memo1/memo_test.go

@@ -0,0 +1,67 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+package memo_test
+
+import (
+	"testing"
+
+	"gopl.io/ch9/memo1"
+	"gopl.io/ch9/memotest"
+)
+
+var httpGetBody = memotest.HTTPGetBody
+
+func Test(t *testing.T) {
+	m := memo.New(httpGetBody)
+	memotest.Sequential(t, m)
+}
+
+// NOTE: not concurrency-safe!  Test fails.
+func TestConcurrent(t *testing.T) {
+	m := memo.New(httpGetBody)
+	memotest.Concurrent(t, m)
+}
+
+/*
+//!+output
+$ go test -v gopl.io/ch9/memo1
+=== RUN   Test
+https://golang.org, 175.026418ms, 7537 bytes
+https://godoc.org, 172.686825ms, 6878 bytes
+https://play.golang.org, 115.762377ms, 5767 bytes
+http://gopl.io, 749.887242ms, 2856 bytes
+
+https://golang.org, 721ns, 7537 bytes
+https://godoc.org, 152ns, 6878 bytes
+https://play.golang.org, 205ns, 5767 bytes
+http://gopl.io, 326ns, 2856 bytes
+--- PASS: Test (1.21s)
+PASS
+ok  gopl.io/ch9/memo1	1.257s
+//!-output
+*/
+
+/*
+//!+race
+$ go test -run=TestConcurrent -race -v gopl.io/ch9/memo1
+=== RUN   TestConcurrent
+...
+WARNING: DATA RACE
+Write by goroutine 36:
+  runtime.mapassign1()
+      ~/go/src/runtime/hashmap.go:411 +0x0
+  gopl.io/ch9/memo1.(*Memo).Get()
+      ~/gobook2/src/gopl.io/ch9/memo1/memo.go:32 +0x205
+  ...
+
+Previous write by goroutine 35:
+  runtime.mapassign1()
+      ~/go/src/runtime/hashmap.go:411 +0x0
+  gopl.io/ch9/memo1.(*Memo).Get()
+      ~/gobook2/src/gopl.io/ch9/memo1/memo.go:32 +0x205
+...
+Found 1 data race(s)
+FAIL	gopl.io/ch9/memo1	2.393s
+//!-race
+*/