[GitHub] [arrow] westonpace commented on a diff in pull request #34133: GH-33856: [C#] C Data interface for schemas and types

["westonpace (via GitHub)" <gi...@apache.org>]

westonpace commented on code in PR #34133:
URL: https://github.com/apache/arrow/pull/34133#discussion_r1121013836


##########
csharp/src/Apache.Arrow/C/CArrowSchema.cs:
##########
@@ -0,0 +1,339 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Apache.Arrow.Types;
+
+[UnmanagedFunctionPointer(CallingConvention.StdCall)]
+public delegate void ReleaseCArrowSchema(IntPtr schema);
+
+namespace Apache.Arrow.C
+{
+    /// <summary>
+    /// An Arrow C Data Interface Schema, which represents a type, field, or schema.
+    /// </summary>
+    /// 
+    /// <remarks>
+    /// This is used to export <see cref="ArrowType"/>, <see cref="Field"/>, or
+    /// <see cref="Schema"/> to other languages. It matches the layout of the
+    /// ArrowSchema struct described in https://github.com/apache/arrow/blob/main/cpp/src/arrow/c/abi.h.
+    /// </remarks>
+    [StructLayout(LayoutKind.Sequential)]
+    unsafe public struct CArrowSchema
+    {
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string format;
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string name;
+        [MarshalAs(UnmanagedType.LPStr)]
+        public string metadata;
+        public long flags;
+        public long n_children;
+        public IntPtr* children;

Review Comment:
   What about [`IntPtr.Size`](https://learn.microsoft.com/en-us/dotnet/api/system.intptr.size?view=net-7.0#system-intptr-size)?
   
   ```
   Marshal.AllocHGlobal(numFields * IntPtr.Size);
   ```



##########
csharp/src/Apache.Arrow/C/CArrowSchema.cs:
##########
@@ -0,0 +1,559 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices;
+using Apache.Arrow.Types;
+
+[UnmanagedFunctionPointer(CallingConvention.StdCall)]

Review Comment:
   Why `StdCall`?



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