From 17a04318715017cdcee25c8863114b82a8114612 Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sun, 14 Dec 2025 21:38:57 +0000
Subject: [PATCH] perf: reduce allocations by pre-sizing list in
 CsvLineSplitter

---
 Csv/CsvLineSplitter.cs |  4 ++--
 Csv/CsvReader.cs       | 16 ++++++++--------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/Csv/CsvLineSplitter.cs b/Csv/CsvLineSplitter.cs
index 48ad845..78f6ab9 100644
--- a/Csv/CsvLineSplitter.cs
+++ b/Csv/CsvLineSplitter.cs
@@ -144,7 +144,7 @@ private static bool IsUnterminatedQuotedValueCore(SpanText value, char quoteChar
             return trailingQuoteCount % 2 != 0;
         }
 
-        public IList<MemoryText> Split(MemoryText line, CsvOptions options)
+        public IList<MemoryText> Split(MemoryText line, CsvOptions options, int? capacity = null)
         {
 #if NET8_0_OR_GREATER
             var span = line.Span;
@@ -152,7 +152,7 @@ public IList<MemoryText> Split(MemoryText line, CsvOptions options)
             var span = line;
 #endif
 
-            var values = new List<MemoryText>();
+            var values = capacity.HasValue ? new List<MemoryText>(capacity.Value) : new List<MemoryText>();
             var start = 0;
             var inQuotes = false;
             char quoteChar = '\0';
diff --git a/Csv/CsvReader.cs b/Csv/CsvReader.cs
index 0f8612d..9407e5b 100644
--- a/Csv/CsvReader.cs
+++ b/Csv/CsvReader.cs
@@ -736,9 +736,9 @@ private static void InitializeOptions(SpanText line, CsvOptions options)
             options.Splitter = CsvLineSplitter.Get(options);
         }
 
-        private static IList<MemoryText> SplitLine(MemoryText line, CsvOptions options)
+        private static IList<MemoryText> SplitLine(MemoryText line, CsvOptions options, int? capacity = null)
         {
-            return options.Splitter.Split(line, options);
+            return options.Splitter.Split(line, options, capacity);
         }
 
         private static MemoryText[] Trim(IList<MemoryText> line, CsvOptions options)
@@ -883,9 +883,9 @@ internal IList<MemoryText> RawSplitLine
                 get
                 {
 #if NET8_0_OR_GREATER
-                    rawSplitLine ??= SplitLine(Raw.AsMemory(), options);
+                    rawSplitLine ??= SplitLine(Raw.AsMemory(), options, headers?.Length);
 #else
-                    rawSplitLine ??= SplitLine(Raw, options);
+                    rawSplitLine ??= SplitLine(Raw, options, headers?.Length);
 #endif
                     return rawSplitLine;
                 }
@@ -982,7 +982,7 @@ public bool LineHasColumn(string name)
                 return RawSplitLine.Count > index;
             }
 
-            internal IList<MemoryText> RawSplitLine => rawSplitLine ??= SplitLine(Raw.AsMemory(), options);
+            internal IList<MemoryText> RawSplitLine => rawSplitLine ??= SplitLine(Raw.AsMemory(), options, headers?.Length);
 
             public string[] Values => Line.Select(it => it.AsString()).ToArray();
             public ReadOnlyMemory<char>[] ValuesMemory => Line;
@@ -1126,7 +1126,7 @@ public bool LineHasColumn(string name)
                 return RawSplitLine.Count > index;
             }
 
-            internal IList<ReadOnlyMemory<char>> RawSplitLine => rawSplitLine ??= SplitLineOptimized(rawMemory, options, memoryOptions);
+            internal IList<ReadOnlyMemory<char>> RawSplitLine => rawSplitLine ??= SplitLineOptimized(rawMemory, options, memoryOptions, headers?.Length);
 
             public string[] Values => Line.Select(v => v.ToString()).ToArray();
             public ReadOnlyMemory<char>[] ValuesMemory => Line;
@@ -1229,10 +1229,10 @@ public bool TryGetSpan(int index, out ReadOnlySpan<char> value)
             public override string ToString() => Raw;
         }
 
-        private static IList<ReadOnlyMemory<char>> SplitLineOptimized(ReadOnlyMemory<char> line, CsvOptions options, CsvMemoryOptions memoryOptions)
+        private static IList<ReadOnlyMemory<char>> SplitLineOptimized(ReadOnlyMemory<char> line, CsvOptions options, CsvMemoryOptions memoryOptions, int? capacity = null)
         {
             var splitter = CsvLineSplitter.Get(options);
-            return splitter.Split(line, options);
+            return splitter.Split(line, options, capacity);
         }
 
         private static ReadOnlyMemory<char>[] TrimOptimized(IList<ReadOnlyMemory<char>> line, CsvOptions options, CsvMemoryOptions memoryOptions)