How to Implement a Queue in Go

Implement a queue in Go by wrapping a slice with a struct that tracks the head index and uses modulo arithmetic for circular behavior. This approach avoids expensive slice copying when removing elements.

package main

import "fmt"

type Queue[T any] struct {
  data []T
  head int
  size int
}

func NewQueue[T any](cap int) *Queue[T] {
  return &Queue[T]{data: make([]T, cap), head: 0, size: 0}
}

func (q *Queue[T]) Enqueue(v T) {
  if q.size == len(q.data) {
    panic("queue full")
  }
  tail := (q.head + q.size) % len(q.data)
  q.data[tail] = v
  q.size++
}

func (q *Queue[T]) Dequeue() (T, bool) {
  if q.size == 0 {
    var zero T
    return zero, false
  }
  v := q.data[q.head]
  q.head = (q.head + 1) % len(q.data)
  q.size--
  return v, true
}

func main() {
  q := NewQueue[int](5)
  q.Enqueue(1)
  q.Enqueue(2)
  v, ok := q.Dequeue()
  fmt.Println(v, ok) // 1 true
}

A queue is like a line at a store: the first person to arrive is the first to be served. In Go, you build this by using a fixed-size list and keeping track of where the front of the line is. This lets you add items to the back and remove them from the front without shifting everyone else in the list.