Add TryAdd to SepWriterHeader (#311)

Author: aaronleev

src/Sep.Test/SepWriterHeaderTest.cs

@@ -163,6 +163,36 @@ public void SepWriterHeaderTest_Add_Twice_Throws()
         Assert.AreEqual("Column name 'A' already exists (Parameter 'colName')", e.Message);
     }
 
+    [TestMethod]
+    public void SepWriterHeaderTest_TryAdd_Once_Is_True()
+    {
+        using var writer = CreateWriter();
+        var header = writer.Header;
+
+        Assert.IsTrue(header.TryAdd("A"));
+    }
+
+    [TestMethod]
+    public void SepWriterHeaderTest_TryAdd_Twice_Is_False()
+    {
+        using var writer = CreateWriter();
+        var header = writer.Header;
+        header.Add("A");
+
+        Assert.IsFalse(header.TryAdd("A"));
+    }
+
+    [TestMethod]
+    public void SepWriterHeaderTest_TryAdd_After_Written_Is_False()
+    {
+        using var writer = CreateWriter();
+        var header = writer.Header;
+        header.Add("A");
+        header.Write();
+
+        Assert.IsFalse(header.TryAdd("B"));
+    }
+
     [TestMethod]
     public void SepWriterHeaderTest_Add_After_Written_Throws()
     {

src/Sep/SepWriterHeader.cs

@@ -45,6 +45,20 @@ public void Add(string colName)
         _writer.AddCol(colName);
     }
 
+    public bool TryAdd(string colName)
+    {
+        if (_writer._headerWrittenOrSkipped)
+        {
+            return false;
+        }
+        if (_writer._colNameToCol.ContainsKey(colName))
+        {
+            return false;
+        }
+        _writer.AddCol(colName);
+        return true;
+    }
+
     public void Write() => _writer.WriteHeader();
     public ValueTask WriteAsync(CancellationToken cancellationToken = default) =>
         _writer.WriteHeaderAsync(cancellationToken);