AK: Add a simple Queue<T> class.

The underlying data structure is a singly-linked list of Vector<T>.
We never shift any of the vector contents around, but we batch the memory
allocations into 1000-element segments.

AK/Queue.h

@@ -0,0 +1,49 @@
+#pragma once
+
+#include <AK/OwnPtr.h>
+#include <AK/SinglyLinkedList.h>
+#include <AK/Vector.h>
+
+namespace AK {
+
+template<typename T>
+class Queue {
+public:
+    Queue() { }
+    ~Queue() { }
+
+    int size() const { return m_size; }
+    bool is_empty() const { return m_size == 0; }
+
+    void enqueue(T&& value)
+    {
+        if (m_segments.is_empty() || m_segments.last()->size() >= segment_size)
+            m_segments.append(make<Vector<T, segment_size>>());
+        m_segments.last()->append(move(value));
+        ++m_size;
+    }
+
+    T dequeue()
+    {
+        ASSERT(!is_empty());
+        auto value = move((*m_segments.first())[m_index_into_first++]);
+        if (m_index_into_first == segment_size) {
+            m_segments.take_first();
+            m_index_into_first = 0;
+        }
+        --m_size;
+        return value;
+    }
+
+private:
+    static const int segment_size = 1000;
+
+    SinglyLinkedList<OwnPtr<Vector<T, segment_size>>> m_segments;
+    int m_index_into_first { 0 };
+    int m_size { 0 };
+};
+
+}
+
+using AK::Queue;
+

AK/SinglyLinkedList.h

@@ -9,7 +9,7 @@ class SinglyLinkedList {
 private:
     struct Node {
         explicit Node(T&& v)
-            : value(v)
+            : value(move(v))
         {
         }
         T value;
@@ -66,7 +66,7 @@ public:
     {
         ASSERT(m_head);
         auto* prev_head = m_head;
-        T value = first();
+        T value = move(first());
         if (m_tail == m_head)
             m_tail = nullptr;
         m_head = m_head->next;

AK/Tests/Makefile

@@ -1,9 +1,12 @@
-all: TestString
+all: TestString TestQueue
 
 CXXFLAGS = -std=c++17 -Wall -Wextra
 
 TestString: TestString.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp TestHelpers.h
 	$(CXX) $(CXXFLAGS) -I../ -I../../ -o $@ TestString.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp
 
+TestQueue: TestQueue.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp TestHelpers.h
+	$(CXX) $(CXXFLAGS) -I../ -I../../ -o $@ TestQueue.cpp ../String.cpp ../StringImpl.cpp ../StringBuilder.cpp ../StringView.cpp
+
 clean:
-	rm -f TestString
+	rm -f TestString TestQueue

AK/Tests/TestQueue.cpp

@@ -0,0 +1,31 @@
+#include "TestHelpers.h"
+#include <AK/AKString.h>
+#include <AK/Queue.h>
+
+int main()
+{
+    EXPECT(Queue<int>().is_empty());
+    EXPECT(Queue<int>().size() == 0);
+
+    Queue<int> ints;
+    ints.enqueue(1);
+    ints.enqueue(2);
+    ints.enqueue(3);
+    EXPECT(ints.size() == 3);
+    EXPECT(ints.dequeue() == 1);
+    EXPECT(ints.size() == 2);
+    EXPECT(ints.dequeue() == 2);
+    EXPECT(ints.size() == 1);
+    EXPECT(ints.dequeue() == 3);
+    EXPECT(ints.size() == 0);
+
+    Queue<String> strings;
+    strings.enqueue("ABC");
+    strings.enqueue("DEF");
+    EXPECT(strings.size() == 2);
+    EXPECT(strings.dequeue() == "ABC");
+    EXPECT(strings.dequeue() == "DEF");
+    EXPECT(strings.is_empty());
+
+    return 0;
+}