queue.go

package queue

// Queue is a FIFO collection.
//
// Concurrency: not safe for concurrent use.
type Queue[T any] struct {
	elements []T
	head     int
}

func (q *Queue[T]) Push(element T) {
	q.elements = append(q.elements, element)
}

func (q *Queue[T]) Pop() (T, bool) {
	if q.head >= len(q.elements) {
		var zero T
		return zero, false
	}
	v := q.elements[q.head]
	q.head++
	if q.head > 1024 && q.head*2 >= len(q.elements) {
		q.elements = append([]T(nil), q.elements[q.head:]...)
		q.head = 0
	}
	return v, true
}

func (q *Queue[T]) Len() int {
	return len(q.elements) - q.head
}

queue_test.go

package queue_test

import (
	"queue"
	"testing"
)

func TestQueue(t *testing.T) {
	queue := &queue.Queue[int]{}
	queue.Push(1)
	queue.Push(2)
	queue.Push(3)
	if l := queue.Len(); l != 3 {
		t.Errorf("Expected 3, got: %v", l)
	}

	if num, _ := queue.Pop(); num != 1 {
		t.Errorf("Expected 1, got: %v", num)
	}
	if num, _ := queue.Pop(); num != 2 {
		t.Errorf("Expected 2, got: %v", num)
	}
	if num, _ := queue.Pop(); num != 3 {
		t.Errorf("Expected 3, got: %v", num)
	}
	if _, ok := queue.Pop(); ok == true {
		t.Errorf("Expected false, got: %v", ok)
	}
	if l := queue.Len(); l != 0 {
		t.Errorf("Expected 0, got: %v", l)
	}

}