What causes "redis: unexpected type=%T for Slice" in go-redis/redis?

Use the typed command method that returns the correct slice shape (LRange → StringSliceCmd; ZRange → StringSliceCmd).

redis: unexpected type=%T for Slice

Error message

redis: unexpected type=%T for Slice

What it means

Returned by Cmd.Slice() (command.go:778) when the reply value is not []interface{}. Slice() expects an array reply already coerced to a Go slice; any scalar type (string, int64, bool, nil) yields this error. Indicates the command did not return an array, or the wrong accessor was used.

Solutions

Use the typed command method that returns the correct slice shape (LRange → StringSliceCmd; ZRange → StringSliceCmd).
Type-switch on cmd.Result() when using Do.
Handle redis.Nil and empty-array cases explicitly before calling Slice().

Example fix

// before
v, err := client.Do(ctx, "LRANGE", "q", 0, -1).Slice()

// after
elems, err := client.LRange(ctx, "q", 0, -1).Result()

Defensive patterns

Strategy: type-guard

Type guard

func asSlice(cmd *redis.Cmd) ([]interface{}, error) {
    if err := cmd.Err(); err != nil { return nil, err }
    if s, ok := cmd.Val().([]interface{}); ok {
        return s, nil
    }
    return nil, fmt.Errorf("not a slice: %T", cmd.Val())
}

Try / catch

s, err := cmd.Slice()
if err != nil && strings.Contains(err.Error(), "unexpected type") {
    // reply was not an array — switch to the typed accessor
}

Prevention

Use StringSliceCmd/Int64SliceCmd-returning methods for array replies.
Type-switch on Result() for raw Do replies.
Handle redis.Nil vs empty-array explicitly.

When it happens

Trigger: Calling Slice() on a Cmd whose reply is a scalar (e.g. Do INCR then Slice()); calling Slice() on a nil reply; using Slice() where the typed accessor (StringSliceCmd, Int64SliceCmd) is required.

Common situations: Generic Do Cmd mis-typed; expecting an array from a command that returns a scalar on a special case (e.g. LRANGE on a non-list returns WRONGTYPE, but a nil/empty case returns nil val); confusing redis.Nil with an empty array.

Related errors

AI-assisted analysis of go-redis/redis@36d97525cd (2026-08-06). Data as JSON: /api/errors/91fd68d935274d48. Report an issue: GitHub.

Appendix: source

Thrown at command.go:787

		return val != 0, nil
	case string:
		return strconv.ParseBool(val)
	default:
		err := fmt.Errorf("redis: unexpected type=%T for Bool", val)
		return false, err
	}
}

func (cmd *Cmd) Slice() ([]interface{}, error) {
	cmd.await()
	if cmd.err != nil {
		return nil, cmd.err
	}
	switch val := cmd.val.(type) {
	case []interface{}:
		return val, nil
	default:
		return nil, fmt.Errorf("redis: unexpected type=%T for Slice", val)
	}
}

func (cmd *Cmd) StringSlice() ([]string, error) {
	slice, err := cmd.Slice()
	if err != nil {
		return nil, err
	}

	ss := make([]string, len(slice))
	for i, iface := range slice {
		val, err := toString(iface)
		if err != nil {
			return nil, err
		}
		ss[i] = val
	}
	return ss, nil

View on GitHub (pinned to 36d97525cd)