geektutu/7days-golang · error

nil Getter

Error message

nil Getter

What it means

Identical to error 90 but in the day4-consistent-hash version: NewGroup panics with "nil Getter" because the Group was constructed without a cache-miss loader. The library requires a non-nil Getter at construction and fails fast rather than nil-panicking later on a cache miss.

Source

Thrown at gee-cache/day4-consistent-hash/geecache/geecache.go:37

}

// A GetterFunc implements Getter with a function.
type GetterFunc func(key string) ([]byte, error)

// Get implements Getter interface function
func (f GetterFunc) Get(key string) ([]byte, error) {
	return f(key)
}

var (
	mu     sync.RWMutex
	groups = make(map[string]*Group)
)

// NewGroup create a new instance of Group
func NewGroup(name string, cacheBytes int64, getter Getter) *Group {
	if getter == nil {
		panic("nil Getter")
	}
	mu.Lock()
	defer mu.Unlock()
	g := &Group{
		name:      name,
		getter:    getter,
		mainCache: cache{cacheBytes: cacheBytes},
	}
	groups[name] = g
	return g
}

// GetGroup returns the named group previously created with NewGroup, or
// nil if there's no such group.
func GetGroup(name string) *Group {
	mu.RLock()
	g := groups[name]
	mu.RUnlock()

View on GitHub (pinned to cf36443821)

Solutions

1. Pass a valid Getter (e.g. geecache.GetterFunc closure) to NewGroup
2. Fix the upstream constructor that returns a typed-nil Getter
3. Add a unit test asserting NewGroup is never called with nil in your wiring code

Example fix

// before
geecache.NewGroup("users", 1<<20, nil) // panic: nil Getter
// after
geecache.NewGroup("users", 1<<20, geecache.GetterFunc(func(key string) ([]byte, error) {
    return fetchUser(key)
}))

if getter == nil {
    panic("NewGroup requires a non-nil Getter")
}
g := geecache.NewGroup("users", 1<<20, getter)

func validGetter(g geecache.Getter) bool {
    return g != nil
}

// Fail fast at startup rather than catching:
if r := recover(); r != nil { log.Fatalf("group init failed: %v", r) }

When it happens

Trigger: geecache.NewGroup(name, cacheBytes, nil) — a nil Getter interface passed directly, or a typed-nil returned from a Getter factory.

Common situations: Getter produced by another subsystem that failed to initialize; variable declared but never assigned; mistaken use of a nil function value instead of a GetterFunc wrapper.

Related errors

• nil Getter
• nil Getter
• nil Getter
• nil Getter
• RegisterPeerPicker called more than once

AI-assisted analysis of geektutu/7days-golang@cf36443821 (2026-09-03). Data as JSON: /api/errors/a47838c6c4137746. Report an issue: GitHub.