From 1bac4afc9bfd023cb574f5e3d537de7c315c7dec Mon Sep 17 00:00:00 2001
From: prozolic <42107886+prozolic@users.noreply.github.com>
Date: Sat, 31 Jan 2026 06:01:27 +0900
Subject: [PATCH] Use Dictionary.TryAdd instead of ContainsKey and indexer by
 reducing lookups. (#917)

* Use Dictionary.TryAdd instead of ContainsKey and indexer by reducing lookups.

* Update src/Markdig/Parsers/ParserList.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
---
 src/Markdig/Helpers/CharacterMap.cs           |  5 +---
 src/Markdig/Parsers/ParserList.cs             |  5 ++--
 src/Markdig/Polyfills/DictionaryExtensions.cs | 23 +++++++++++++++++++
 .../Syntax/LinkReferenceDefinitionGroup.cs    |  5 +---
 4 files changed, 27 insertions(+), 11 deletions(-)
 create mode 100644 src/Markdig/Polyfills/DictionaryExtensions.cs

diff --git a/src/Markdig/Helpers/CharacterMap.cs b/src/Markdig/Helpers/CharacterMap.cs
index 73ed3322..a33562ec 100644
--- a/src/Markdig/Helpers/CharacterMap.cs
+++ b/src/Markdig/Helpers/CharacterMap.cs
@@ -51,10 +51,7 @@ public sealed class CharacterMap<T> where T : class
             {
                 nonAsciiMap ??= [];
 
-                if (!nonAsciiMap.ContainsKey(openingChar))
-                {
-                    nonAsciiMap[openingChar] = state.Value;
-                }
+                nonAsciiMap.TryAdd(openingChar, state.Value);
             }
         }
 
diff --git a/src/Markdig/Parsers/ParserList.cs b/src/Markdig/Parsers/ParserList.cs
index ec0db494..3d52ee5b 100644
--- a/src/Markdig/Parsers/ParserList.cs
+++ b/src/Markdig/Parsers/ParserList.cs
@@ -38,11 +38,10 @@ public abstract class ParserList<T, TState> : OrderedList<T> where T : notnull,
             {
                 foreach (var openingChar in parser.OpeningCharacters)
                 {
-                    if (!charCounter.ContainsKey(openingChar))
+                    if (!charCounter.TryAdd(openingChar, 1))
                     {
-                        charCounter[openingChar] = 0;
+                        charCounter[openingChar]++;
                     }
-                    charCounter[openingChar]++;
                 }
             }
             else
diff --git a/src/Markdig/Polyfills/DictionaryExtensions.cs b/src/Markdig/Polyfills/DictionaryExtensions.cs
new file mode 100644
index 00000000..fbf6f2a4
--- /dev/null
+++ b/src/Markdig/Polyfills/DictionaryExtensions.cs
@@ -0,0 +1,23 @@
+// Copyright (c) Alexandre Mutel. All rights reserved.
+// This file is licensed under the BSD-Clause 2 license.
+// See the license.txt file in the project root for more information.
+
+#if !(NETSTANDARD2_1_OR_GREATER || NET)
+
+namespace System.Collections.Generic;
+
+internal static class DictionaryExtensions
+{
+    public static bool TryAdd<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key, TValue value) where TKey : notnull
+    {
+        if (!dictionary.ContainsKey(key))
+        {
+            dictionary[key] = value;
+            return true;
+        }
+
+        return false;
+    }
+}
+
+#endif
diff --git a/src/Markdig/Syntax/LinkReferenceDefinitionGroup.cs b/src/Markdig/Syntax/LinkReferenceDefinitionGroup.cs
index 9f79636a..b942ab6e 100644
--- a/src/Markdig/Syntax/LinkReferenceDefinitionGroup.cs
+++ b/src/Markdig/Syntax/LinkReferenceDefinitionGroup.cs
@@ -40,10 +40,7 @@ public class LinkReferenceDefinitionGroup : ContainerBlock
         if (!Contains(link))
         {
             Add(link);
-            if (!Links.ContainsKey(label))
-            {
-                Links[label] = link;
-            }
+            Links.TryAdd(label, link);
         }
     }