Reduce a bit of LINQ in M.E.AI (#5663)

src/Libraries/Microsoft.Extensions.AI.Abstractions/AdditionalPropertiesDictionary.cs

@@ -111,7 +111,8 @@ public sealed class AdditionalPropertiesDictionary : IDictionary<string, object?
     public void Clear() => _dictionary.Clear();
 
     /// <inheritdoc />
-    bool ICollection<KeyValuePair<string, object?>>.Contains(KeyValuePair<string, object?> item) => _dictionary.Contains(item);
+    bool ICollection<KeyValuePair<string, object?>>.Contains(KeyValuePair<string, object?> item) =>
+        ((ICollection<KeyValuePair<string, object?>>)_dictionary).Contains(item);
 
     /// <inheritdoc />
     public bool ContainsKey(string key) => _dictionary.ContainsKey(key);

src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatMessage.cs

@@ -3,7 +3,6 @@
 
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Linq;
 using System.Text.Json.Serialization;
 using Microsoft.Shared.Diagnostics;
 
@@ -60,10 +59,10 @@ public class ChatMessage
     [JsonIgnore]
     public string? Text
     {
-        get => Contents.OfType<TextContent>().FirstOrDefault()?.Text;
+        get => Contents.FindFirst<TextContent>()?.Text;
         set
         {
-            if (Contents.OfType<TextContent>().FirstOrDefault() is { } textContent)
+            if (Contents.FindFirst<TextContent>() is { } textContent)
             {
                 textContent.Text = value;
             }
@@ -95,6 +94,5 @@ public class ChatMessage
     public AdditionalPropertiesDictionary? AdditionalProperties { get; set; }
 
     /// <inheritdoc/>
-    public override string ToString() =>
-        string.Concat(Contents.OfType<TextContent>());
+    public override string ToString() => Contents.ConcatText();
 }

src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/StreamingChatCompletionUpdate.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
-using System.Linq;
 using System.Text.Json.Serialization;
 
 namespace Microsoft.Extensions.AI;
@@ -66,10 +65,10 @@ public class StreamingChatCompletionUpdate
     [JsonIgnore]
     public string? Text
     {
-        get => Contents.OfType<TextContent>().FirstOrDefault()?.Text;
+        get => Contents.FindFirst<TextContent>()?.Text;
         set
         {
-            if (Contents.OfType<TextContent>().FirstOrDefault() is { } textContent)
+            if (Contents.FindFirst<TextContent>() is { } textContent)
             {
                 textContent.Text = value;
             }
@@ -116,6 +115,5 @@ public class StreamingChatCompletionUpdate
     public string? ModelId { get; set; }
 
     /// <inheritdoc/>
-    public override string ToString() =>
-        string.Concat(Contents.OfType<TextContent>());
+    public override string ToString() => Contents.ConcatText();
 }

src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/AIContentExtensions.cs

@@ -0,0 +1,64 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+#if !NET
+using System.Linq;
+#else
+using System.Runtime.CompilerServices;
+#endif
+
+namespace Microsoft.Extensions.AI;
+
+/// <summary>Internal extensions for working with <see cref="AIContent"/>.</summary>
+internal static class AIContentExtensions
+{
+    /// <summary>Finds the first occurrence of a <typeparamref name="T"/> in the list.</summary>
+    public static T? FindFirst<T>(this IList<AIContent> contents)
+        where T : AIContent
+    {
+        int count = contents.Count;
+        for (int i = 0; i < count; i++)
+        {
+            if (contents[i] is T t)
+            {
+                return t;
+            }
+        }
+
+        return null;
+    }
+
+    /// <summary>Concatenates the text of all <see cref="TextContent"/> instances in the list.</summary>
+    public static string ConcatText(this IList<AIContent> contents)
+    {
+        int count = contents.Count;
+        switch (count)
+        {
+            case 0:
+                break;
+
+            case 1:
+                return contents[0] is TextContent tc ? tc.Text : string.Empty;
+
+            default:
+#if NET
+                DefaultInterpolatedStringHandler builder = new(0, 0, null, stackalloc char[512]);
+                for (int i = 0; i < count; i++)
+                {
+                    if (contents[i] is TextContent text)
+                    {
+                        builder.AppendLiteral(text.Text);
+                    }
+                }
+
+                return builder.ToStringAndClear();
+#else
+                return string.Concat(contents.OfType<TextContent>());
+#endif
+        }
+
+        return string.Empty;
+    }
+}

src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs

@@ -502,7 +502,7 @@ public sealed partial class OpenTelemetryChatClient : DelegatingChatClient
     {
         if (EnableSensitiveData)
         {
-            string content = string.Concat(message.Contents.OfType<TextContent>().Select(c => c.Text));
+            string content = string.Concat(message.Contents.OfType<TextContent>());
             if (content.Length > 0)
             {
                 return content;