Transition to using explicit nullable types (#184)

Bearded.Utilities/Algorithms/CoffmanGraham.cs

@@ -177,7 +177,7 @@ private static ImmutableList<ImmutableHashSet<T>> createLayers<T>(
 
     public static ISolver SolverForReducedGraphs(int maxLayerSize) => new ReducedGraphSolver(maxLayerSize);
 
-    private struct DecreasingNumberSequence : IComparable<DecreasingNumberSequence>, IComparable
+    private readonly struct DecreasingNumberSequence : IComparable<DecreasingNumberSequence>, IComparable
     {
         private readonly ImmutableList<int> numbers;
 
@@ -186,7 +186,7 @@ private DecreasingNumberSequence(ImmutableList<int> numbers)
             this.numbers = numbers;
         }
 
-        public int CompareTo(object obj) => CompareTo((DecreasingNumberSequence) obj);
+        public int CompareTo(object? obj) => CompareTo((DecreasingNumberSequence) (obj ?? throw new ArgumentNullException()));
 
         public int CompareTo(DecreasingNumberSequence other)
         {

Bearded.Utilities/Collections/DeletableObjectList.cs

@@ -16,7 +16,7 @@ public sealed class DeletableObjectList<T> : IEnumerable<T>
 {
     #region Fields and Properties
 
-    private readonly List<T> list;
+    private readonly List<T?> list;
 
     private int enumerators;
     private int count;
@@ -47,7 +47,7 @@ public DeletableObjectList()
 
     public DeletableObjectList(int capacity)
     {
-        list = new List<T>(capacity);
+        list = new List<T?>(capacity);
         MaxEmptyFraction = 0.2f;
     }
 

Bearded.Utilities/Collections/DeletableObjectListEnumerator.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 
 namespace Bearded.Utilities.Collections;
@@ -10,13 +11,19 @@ internal class DeletableObjectListEnumerator<T> : IEnumerator<T>
     where T : class, IDeletable
 {
     private readonly DeletableObjectList<T> deletableObjectList;
-    private readonly List<T> list;
+    private readonly List<T?> list;
     private int i;
+    private T? current;
 
     object System.Collections.IEnumerator.Current => Current;
-    public T Current { get; private set; }
 
-    public DeletableObjectListEnumerator(DeletableObjectList<T> deletableObjectList, List<T> list)
+    public T Current
+    {
+        get => current ?? throw new InvalidOperationException();
+        private set => current = value;
+    }
+
+    public DeletableObjectListEnumerator(DeletableObjectList<T> deletableObjectList, List<T?> list)
     {
         this.deletableObjectList = deletableObjectList;
         this.list = list;

Bearded.Utilities/Collections/MutableLinkedList.cs

@@ -13,12 +13,11 @@ public sealed class MutableLinkedList<T> : IEnumerable<T>
 {
     #region Fields and Properties
 
-    private readonly LinkedList<MutableLinkedListEnumerator<T>> enumerators =
-        new LinkedList<MutableLinkedListEnumerator<T>>();
+    private readonly LinkedList<MutableLinkedListEnumerator<T>> enumerators = new();
 
-    public MutableLinkedListNode<T> First { get; private set; }
+    public MutableLinkedListNode<T>? First { get; private set; }
 
-    public MutableLinkedListNode<T> Last { get; private set; }
+    public MutableLinkedListNode<T>? Last { get; private set; }
 
     public int Count { get; private set; }
 
@@ -56,7 +55,7 @@ public void Add(MutableLinkedListNode<T> node)
         else
         {
             node.Prev = Last;
-            Last.Next = node;
+            Last!.Next = node; // We know that Last is not null here, as the list is not empty.
         }
 
         Last = node;
@@ -147,7 +146,7 @@ public void InsertBefore(MutableLinkedListNode<T> node, MutableLinkedListNode<T>
             throw new ArgumentException("Object must already be in list before inserting.");
         if (beforeThis.List != this)
             throw new ArgumentException("The object to insert before must be in the same list.");
-        if (node != Last)
+        if (node != Last || node.Prev == null)
             throw new ArgumentException("Inserted object must be last object in list.");
         if (node == beforeThis)
             throw new ArgumentException("Cannot insert object before itself.");
@@ -173,7 +172,7 @@ public IEnumerator<T> GetEnumerator()
     {
         var e = new MutableLinkedListEnumerator<T>(this);
         enumerators.AddFirst(e);
-        e.SetNode(enumerators.First);
+        e.SetNode(enumerators.First!); // We know First is not null as we just added e
         return e;
     }
 

Bearded.Utilities/Collections/MutableLinkedListEnumerator.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 
 namespace Bearded.Utilities.Collections;
@@ -21,19 +22,15 @@ public MutableLinkedListEnumerator(MutableLinkedList<T> list)
         this.list = list;
     }
 
-    private LinkedListNode<MutableLinkedListEnumerator<T>> node;
+    private LinkedListNode<MutableLinkedListEnumerator<T>>? node;
     public void SetNode(LinkedListNode<MutableLinkedListEnumerator<T>> node)
     {
-        if (this.node == null)
-            this.node = node;
+        this.node ??= node;
     }
 
-    public T Current
-    {
-        get { return current.Value; }
-    }
+    public T Current => current?.Value ?? throw new InvalidOperationException();
 
-    private MutableLinkedListNode<T> current;
+    private MutableLinkedListNode<T>? current;
 
     public void OnObjectRemove(MutableLinkedListNode<T> obj)
     {
@@ -48,6 +45,8 @@ public void OnObjectRemove(MutableLinkedListNode<T> obj)
 
     public void Dispose()
     {
+        if (node is null) return;
+
         list.ForgetEnumerator(node);
     }
 
@@ -69,12 +68,14 @@ public bool MoveNext()
                 currentWasDeleted = false;
                 return true;
             }
-            current = current.Next;
-            if (current == null)
+
+            if (current?.Next == null)
             {
                 done = true;
                 return false;
             }
+
+            current = current.Next;
         }
         return true;
     }
@@ -87,9 +88,5 @@ public void Reset()
         currentWasDeleted = false;
     }
 
-    object System.Collections.IEnumerator.Current
-    {
-        get { return Current; }
-    }
-
+    object System.Collections.IEnumerator.Current => Current;
 }

Bearded.Utilities/Collections/MutableLinkedListNode.cs

@@ -1,4 +1,6 @@
 
+using System;
+
 namespace Bearded.Utilities.Collections;
 
 /// <summary>
@@ -25,23 +27,21 @@ public class MutableLinkedListNode<T>
 
     #region Fields and Properties
 
-    private readonly T value;
-
     /// <summary>
     /// The value stored in the node.
     /// </summary>
-    public T Value { get { return value; } }
+    public T? Value { get; }
 
     // Next, Prev and List are internally writeable to
     // simplify addition, removal and insertion code.
     // Do not mess with them!
-    internal MutableLinkedListNode<T> Next { get; set; }
-    internal MutableLinkedListNode<T> Prev { get; set; }
+    internal MutableLinkedListNode<T>? Next { get; set; }
+    internal MutableLinkedListNode<T>? Prev { get; set; }
 
     /// <summary>
     /// The list the node is part of.
     /// </summary>
-    public MutableLinkedList<T> List { get; internal set; }
+    public MutableLinkedList<T>? List { get; internal set; }
 
     internal bool ChangingList { get; private set; }
 
@@ -51,12 +51,12 @@ public class MutableLinkedListNode<T>
 
     internal MutableLinkedListNode(T value)
     {
-        this.value = value;
+        Value = value;
     }
 
     internal MutableLinkedListNode()
     {
-        value = this as T;
+        Value = this as T;
     }
 
     #endregion
@@ -89,15 +89,15 @@ public void AddToListBefore(MutableLinkedList<T> list, MutableLinkedListNode<T>
     /// <param name="beforeThis">The node to add this before.</param>
     public void InsertBefore(MutableLinkedListNode<T> beforeThis)
     {
-        List.InsertBefore(this, beforeThis);
+        List?.InsertBefore(this, beforeThis);
     }
 
     /// <summary>
     /// Removes this node from the list it is in.
     /// </summary>
     public void RemoveFromList()
     {
-        List.Remove(this);
+        List?.Remove(this);
     }
 
     #endregion

Bearded.Utilities/Collections/PrefixTrie.cs

@@ -13,7 +13,7 @@ private struct Node
     {
         private readonly Dictionary<char, Node>? values;
 
-        public string Key { get; }
+        public string? Key { get; }
 
         #region creating
 

Bearded.Utilities/Collections/PriorityQueue.cs

@@ -9,7 +9,9 @@ namespace Bearded.Utilities.Collections;
 /// </summary>
 /// <typeparam name="TPriority"></typeparam>
 /// <typeparam name="TValue"></typeparam>
-public sealed class PriorityQueue<TPriority, TValue> : StaticPriorityQueue<TPriority, TValue> where TPriority : IComparable<TPriority>
+public sealed class PriorityQueue<TPriority, TValue> : StaticPriorityQueue<TPriority, TValue>
+    where TPriority : IComparable<TPriority>
+    where TValue : notnull
 {
     private readonly Dictionary<TValue, int> valueDict = new Dictionary<TValue, int>();
 

Bearded.Utilities/Core/Environment.cs

@@ -43,7 +43,7 @@ private static Platform detectPlatform()
     #endregion
 
     #region User settings directory
-    private static string userSettingsDirectory;
+    private static string? userSettingsDirectory;
 
     private static string buildUserSettingsDirectory()
     {
@@ -67,8 +67,7 @@ private static string buildUserSettingsDirectory()
                     return linuxConfigDir;
 
                 var linuxHomeDir = System.Environment.GetEnvironmentVariable("HOME");
-                // ReSharper disable once AssignNullToNotNullAttribute
-                return string.IsNullOrEmpty(linuxConfigDir) ? "." : Path.Combine(linuxHomeDir, ".config");
+                return string.IsNullOrEmpty(linuxConfigDir) ? "." : Path.Combine(linuxHomeDir!, ".config");
             default:
                 throw new InvalidOperationException("Encountered unknown platform.");
         }
@@ -80,7 +79,7 @@ private static string buildUserSettingsDirectory()
     /// For OSX: ~/Library/Application Support
     /// For Linux: ~/.config
     /// </summary>
-    public static string UserSettingsDirectory => userSettingsDirectory ?? (userSettingsDirectory = buildUserSettingsDirectory());
+    public static string UserSettingsDirectory => userSettingsDirectory ??= buildUserSettingsDirectory();
 
     /// <summary>
     /// Gets the default user setting directory for a given game name.