You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: memo.go
    path of file: ./repos/learning/golang/source_code/gopl.io/ch9/memo3
    
    the code of the file until where you have to start completion: // Copyright Â© 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// See page 276.

// Package memo provides a concurrency-safe memoization a function of
// type Func.  Reque
    
func (memo *Memo) Get(key string) (value interface{}, err error) {
	memo.mu.Lock()
	res, ok := memo.cache[key]
	memo.mu.Unlock()
	if !ok {
		res.value, res.err = memo.f(key)

		// Between the two critical sections, several goroutines
		// may race to compute f(key) and update the map.
		memo.mu.Lock()
		memo.cache[key] = res
		memo.mu.Unlock()
	}
	return res.value, res.err
}