Use string interning for fun and performance

YamlDotNet/Core/AnchorName.cs

@@ -39,12 +39,17 @@ namespace YamlDotNet.Core
 
         public AnchorName(string value)
         {
-            this.value = value ?? throw new ArgumentNullException(nameof(value));
+            if (value != null)
+            {
+                throw new ArgumentNullException(nameof(value));
+            }
 
             if (!AnchorPattern.IsMatch(value))
             {
                 throw new ArgumentException($"Anchor cannot be empty or contain disallowed characters: []{{}},\nThe value was '{value}'.", nameof(value));
             }
+
+            this.value = string.Intern(value);
         }
 
         public override string ToString() => value ?? "[empty]";

YamlDotNet/Core/Events/Scalar.cs

@@ -79,7 +79,7 @@ public sealed class Scalar : NodeEvent
         public Scalar(AnchorName anchor, TagName tag, string value, ScalarStyle style, bool isPlainImplicit, bool isQuotedImplicit, Mark start, Mark end, bool isKey = false)
             : base(anchor, tag, start, end)
         {
-            this.Value = value;
+            this.Value = (isKey || value.Length < 40) ? string.Intern(value) : value;
             this.Style = style;
             this.IsPlainImplicit = isPlainImplicit;
             this.IsQuotedImplicit = isQuotedImplicit;

YamlDotNet/Core/TagName.cs

@@ -39,7 +39,7 @@ namespace YamlDotNet.Core
 
         public TagName(string value)
         {
-            this.value = value ?? throw new ArgumentNullException(nameof(value));
+            this.value = string.Intern(value);
 
             if (value.Length == 0)
             {