Update Extensions.cs

Author: SimonCropp

src/Verify/Extensions.cs

@@ -1,5 +1,7 @@
 // ReSharper disable UnusedVariable
 
+public delegate bool RemoveLine(CharSpan line);
+
 static class Extensions
 {
     static HashSet<Type> numericTypes =
@@ -152,26 +154,32 @@ public static string NameWithParent(this Type type)
         return null;
     }
 
-    public static void FilterLines(this StringBuilder input, Func<string, bool> removeLine)
+    // public static void FilterLines(this StringBuilder input, Func<string, bool> removeLine) =>
+    //     FilterLines(input, (CharSpan line) => removeLine(line.ToString()));
+
+    public static void FilterLines(this StringBuilder input, RemoveLine removeLine)
     {
-        var theString = input.ToString();
-        using var reader = new StringReader(theString);
+        if (input.Length == 0)
+        {
+            return;
+        }
+
+        var span = input.AsSpan();
+        var hasTrailingNewline = span[^1] == '\n';
+
         input.Clear();
 
-        while (reader.ReadLine() is { } line)
+        foreach (var line in span.EnumerateLines())
         {
-            if (removeLine(line))
+            if (!removeLine(line))
             {
-                continue;
+                input.AppendLineN(line);
             }
-
-            input.AppendLineN(line);
         }
 
-        if (input.Length > 0 &&
-            !theString.EndsWith('\n'))
+        if (input.Length > 0 && !hasTrailingNewline)
         {
-            input.Length -= 1;
+            input.Length--;
         }
     }