memo.go
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memo.go
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	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
	}