Mono Fix for Unsafe Mode (#4887)

* Added preprocessor define for C++ if Template Aliases are supported by the compiler

* Revert "Revert "Performance Increase of Vector of Structures using .NET BlockCopy (#4830)""

This reverts commit 1f5eae5d6a135ff6811724f6c57f911d1f46bb15.

* Put<T> method was inside #if UNSAFE_BYTEBUFFER which caused compilation failure when building in unsafe mode

* Revert "Added preprocessor define for C++ if Template Aliases are supported by the compiler"

This reverts commit a75af7352127c261baf0b6cca5cb823e13e78f11.

3 files changed, 182 insertions, 4 deletions

diff --git a/net/FlatBuffers/ByteBuffer.cs b/net/FlatBuffers/ByteBuffer.cs
index 878e740b..7b170c17 100644
--- a/net/FlatBuffers/ByteBuffer.cs
+++ b/net/FlatBuffers/ByteBuffer.cs
@@ -30,6 +30,7 @@
 //
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Text;
 
@@ -91,19 +92,78 @@ namespace FlatBuffers
 
         public byte[] ToArray(int pos, int len)
         {
-            byte[] arr = new byte[len];
-            Buffer.BlockCopy(_buffer, pos, arr, 0, len);
+            return ToArray<byte>(pos, len);
+        }
+
+        /// <summary>
+        /// A lookup of type sizes. Used instead of Marshal.SizeOf() which has additional
+        /// overhead, but also is compatible with generic functions for simplified code.
+        /// </summary>
+        private static Dictionary<Type, int> genericSizes = new Dictionary<Type, int>()
+        {
+            { typeof(bool),     sizeof(bool) },
+            { typeof(float),    sizeof(float) },
+            { typeof(double),   sizeof(double) },
+            { typeof(sbyte),    sizeof(sbyte) },
+            { typeof(byte),     sizeof(byte) },
+            { typeof(short),    sizeof(short) },
+            { typeof(ushort),   sizeof(ushort) },
+            { typeof(int),      sizeof(int) },
+            { typeof(uint),     sizeof(uint) },
+            { typeof(ulong),    sizeof(ulong) },
+            { typeof(long),     sizeof(long) },
+        };
+
+        /// <summary>
+        /// Get the wire-size (in bytes) of a type supported by flatbuffers.
+        /// </summary>
+        /// <param name="t">The type to get the wire size of</param>
+        /// <returns></returns>
+        public static int SizeOf<T>()
+        {
+            return genericSizes[typeof(T)];
+        }
+
+        /// <summary>
+        /// Checks if the Type provided is supported as scalar value
+        /// </summary>
+        /// <typeparam name="T">The Type to check</typeparam>
+        /// <returns>True if the type is a scalar type that is supported, falsed otherwise</returns>
+        public static bool IsSupportedType<T>()
+        {
+            return genericSizes.ContainsKey(typeof(T));
+        }
+
+        /// <summary>
+        /// Get the wire-size (in bytes) of an typed array
+        /// </summary>
+        /// <typeparam name="T">The type of the array</typeparam>
+        /// <param name="x">The array to get the size of</param>
+        /// <returns>The number of bytes the array takes on wire</returns>
+        public static int ArraySize<T>(T[] x)
+        {
+            return SizeOf<T>() * x.Length;
+        }
+
+        // Get a portion of the buffer casted into an array of type T, given
+        // the buffer position and length.
+        public T[] ToArray<T>(int pos, int len)
+            where T: struct
+        {
+            AssertOffsetAndLength(pos, len);
+            T[] arr = new T[len];
+            Buffer.BlockCopy(_buffer, pos, arr, 0, ArraySize(arr));
             return arr;
         }
 
         public byte[] ToSizedArray()
         {
-            return ToArray(Position, Length - Position);
+            return ToArray<byte>(Position, Length - Position);
         }
 
         public byte[] ToFullArray()
         {
-            return ToArray(0, Length);
+            return ToArray<byte>(0, Length);
         }
 
         public ArraySegment<byte> ToArraySegment(int pos, int len)
@@ -370,6 +430,58 @@ namespace FlatBuffers
 
 #endif // UNSAFE_BYTEBUFFER
 
+        /// <summary>
+        /// Copies an array of type T into this buffer, ending at the given
+        /// offset into this buffer. The starting offset is calculated based on the length
+        /// of the array and is the value returned.
+        /// </summary>
+        /// <typeparam name="T">The type of the input data (must be a struct)</typeparam>
+        /// <param name="offset">The offset into this buffer where the copy will end</param>
+        /// <param name="x">The array to copy data from</param>
+        /// <returns>The 'start' location of this buffer now, after the copy completed</returns>
+        public int Put<T>(int offset, T[] x)
+            where T : struct
+        {
+            if(x == null)
+            {
+                throw new ArgumentNullException("Cannot put a null array");
+            }
+
+            if(x.Length == 0)
+            {
+                throw new ArgumentException("Cannot put an empty array");
+            }
+
+            if(!IsSupportedType<T>())
+            {
+                throw new ArgumentException("Cannot put an array of type "
+                    + typeof(T) + " into this buffer");
+            }
+
+            if (BitConverter.IsLittleEndian)
+            {
+                int numBytes = ByteBuffer.ArraySize(x);
+                offset -= numBytes;
+                AssertOffsetAndLength(offset, numBytes);
+                // if we are LE, just do a block copy
+                Buffer.BlockCopy(x, 0, _buffer, offset, numBytes);
+            }
+            else
+            {
+                throw new NotImplementedException("Big Endian Support not implemented yet " +
+                    "for putting typed arrays");
+                // if we are BE, we have to swap each element by itself
+                //for(int i = x.Length - 1; i >= 0; i--)
+                //{
+                //  todo: low priority, but need to genericize the Put<T>() functions
+                //}
+            }
+            return offset;
+        }
+
+
+
+
         public sbyte GetSbyte(int index)
         {
             AssertOffsetAndLength(index, sizeof(sbyte));
diff --git a/net/FlatBuffers/FlatBufferBuilder.cs b/net/FlatBuffers/FlatBufferBuilder.cs
index a2224498..33bba969 100644
--- a/net/FlatBuffers/FlatBufferBuilder.cs
+++ b/net/FlatBuffers/FlatBufferBuilder.cs
@@ -179,6 +179,18 @@ namespace FlatBuffers
             _bb.PutFloat(_space -= sizeof(float), x);
         }
 
+        /// <summary>
+        /// Puts an array of type T into this builder at the 
+        /// current offset
+        /// </summary>
+        /// <typeparam name="T">The type of the input data </typeparam>
+        /// <param name="x">The array to copy data from</param>
+        public void Put<T>(T[] x)
+            where T : struct
+        {
+            _space = _bb.Put(_space, x);
+        }
+
         public void PutDouble(double x)
         {
             _bb.PutDouble(_space -= sizeof(double), x);
@@ -246,6 +258,37 @@ namespace FlatBuffers
         public void AddFloat(float x) { Prep(sizeof(float), 0); PutFloat(x); }
 
         /// <summary>
+        /// Add an array of type T to the buffer (aligns the data and grows if necessary).
+        /// </summary>
+        /// <typeparam name="T">The type of the input data</typeparam>
+        /// <param name="x">The array to copy data from</param>
+        public void Add<T>(T[] x)
+            where T : struct
+        {
+            if (x == null)
+            {
+                throw new ArgumentNullException("Cannot add a null array");
+            }
+
+            if( x.Length == 0)
+            {
+                // don't do anything if the array is empty
+                return;
+            }
+
+            if(!ByteBuffer.IsSupportedType<T>())
+            {
+                throw new ArgumentException("Cannot add this Type array to the builder");
+            }
+
+            int size = ByteBuffer.SizeOf<T>();
+            // Need to prep on size (for data alignment) and then we pass the
+            // rest of the length (minus 1) as additional bytes
+            Prep(size, size * (x.Length - 1));
+            Put(x);
+        }
+
+        /// <summary>
         /// Add a `double` to the buffer (aligns the data and grows if necessary).
         /// </summary>
         /// <param name="x">The `double` to add to the buffer.</param>
diff --git a/net/FlatBuffers/Table.cs b/net/FlatBuffers/Table.cs
index 4a188ff8..07db5f42 100644
--- a/net/FlatBuffers/Table.cs
+++ b/net/FlatBuffers/Table.cs
@@ -94,6 +94,29 @@ namespace FlatBuffers
             return bb.ToArraySegment(pos, len);
         }
 
+        // Get the data of a vector whoses offset is stored at "offset" in this object as an
+        // T[]. If the vector is not present in the ByteBuffer, then a null value will be
+        // returned.
+        public T[] __vector_as_array<T>(int offset)
+            where T : struct
+        {
+            if(!BitConverter.IsLittleEndian)
+            {
+                throw new NotSupportedException("Getting typed arrays on a Big Endian " +
+                    "system is not support");
+            }
+
+            var o = this.__offset(offset);
+            if (0 == o)
+            {
+                return null;
+            }
+
+            var pos = this.__vector(o);
+            var len = this.__vector_len(o);
+            return bb.ToArray<T>(pos, len);
+        }
+
         // Initialize any Table-derived type to point to the union at the given offset.
         public T __union<T>(int offset) where T : struct, IFlatbufferObject
         {