# Spot the bug: Go

> One snippet. Find the bug, or prove there isn't one.

Daily challenge: 2026-08-19 (UTC) · Mid-Level

```go
package users

import "sync"

type User struct {
	ID   string
	Name string
}

var (
	mu    sync.Mutex
	cache = map[string]*User{}
)

func GetUser(id string, fetch func() *User) *User {
	mu.Lock()
	defer mu.Unlock()
	if u, ok := cache[id]; ok {
		return u
	}
	u := fetch()
	cache[id] = u
	return u
}
```

## Your verdict

- Security flaw
- Logic bug
- Code style
- No issue

One attempt per day. The answer shows up right after.

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