TheAlgorithms/Go · warning

ErrEmptyDequeue

ErrEmptyDequeue

Error message

DoublyEnded queue is empty, so can't perform this operation

What it means

ErrEmptyDequeue is the package-level sentinel error returned by every read/remove operation (DequeueFront, DequeueRear, Front, Rear) on a DoublyEndedQueue that holds no elements. It prevents index panics when accessing dq.deque[0] or the last element of an empty slice.

Source

Thrown at structure/deque/deque.go:15

// description: Double Ended Queue is a generalized version of Queue data structure that allows insert and delete at both ends.
// References:
//	Wikipedia : https://en.wikipedia.org/wiki/Double-ended_queue
//	Github: https://www.geeksforgeeks.org/deque-set-1-introduction-applications/
// author [Sayan](https://github.com/bose-sayan)

// Package deque implements a Double Ended Queue data structure.
package deque

import (
	"errors"
)

// ErrEmptyDequeue is a custom error for handling cases when some dequeuing operation is performed on an empty deque.
var ErrEmptyDequeue = errors.New("DoublyEnded queue is empty, so can't perform this operation")

type DoublyEndedQueue[T any] struct {
	deque []T
}

// New returns a new DoublyEndedQueue.
func New[T any]() *DoublyEndedQueue[T] {
	return &DoublyEndedQueue[T]{deque: make([]T, 0)}
}

// EnqueueFront adds an item at the front of Deque.
func (dq *DoublyEndedQueue[T]) EnqueueFront(item T) {
	dq.deque = append([]T{item}, dq.deque...)
}

// EnqueueRear adds an item at the rear of Deque.
func (dq *DoublyEndedQueue[T]) EnqueueRear(item T) {
	dq.deque = append(dq.deque, item)

View on GitHub (pinned to 5ba447ec5f)

Solutions

1. Compare the returned error against ErrEmptyDequeue (errors.Is) and treat it as an empty signal
2. Check the deque length or add an IsEmpty helper before popping
3. Restructure to a blocking approach (channel) if consumers must wait for items

Example fix

// before
v, _ := dq.DequeueFront()
use(v) // zero value when empty
// after
v, err := dq.DequeueFront()
if errors.Is(err, deque.ErrEmptyDequeue) {
    return // deque is empty
}
use(v)

if len(dq.Deque()) == 0 {
    return deque.ErrEmptyDequeue
}

func isErrEmptyDequeue(err error) bool { return errors.Is(err, deque.ErrEmptyDequeue) }

v, err := dq.DequeueRear()
if errors.Is(err, deque.ErrEmptyDequeue) {
    return // deque drained
}
if err != nil {
    return err
}

When it happens

Trigger: Calling Front, Rear, DequeueFront, or DequeueRear when len(dq.deque) == 0 — e.g. on a queue created with New() but never populated, or after draining all elements.

Common situations: Consumer loops draining a deque until empty; popping both ends of a work-stealing deque without a size check; test code that forgot to seed the deque.

Related errors

• queue is empty
• empty slice provided
• size must be greater than 0
• queue is full
• index out of range

AI-assisted analysis of TheAlgorithms/Go@5ba447ec5f (2026-09-02). Data as JSON: /api/errors/e2426d517af93da7. Report an issue: GitHub.