Question

I need to pass value from array to method that has where T : struct generic constraint.

I have object[] values; That for example contains { (int)7, (byte)3, (char)'a' } (i don’t know structure at compile time)

and i need to pass that array, or all elements one by one to any of following methods

DataStream(Array array)
DataStream(IntPtr ptrToArray, int sizeInbytes)

DataStream.Write<T>(T value) where T : struct
DataStream.WriteBytes(byte[] bytes)

First method will write some error in GCHandle.Alloc (that object does not contain primitive data)
Third mthod will not compile since object is not struct

Actual problem is that i am trying to create MeshBuilder in SlimDX that will contain VertexChannels and then build VertexBuffer out of them

Answer 1

Well, your array will contain boxed values which is why the first two will fail. You’re not going to be able to do this all in one call.

Options:

• Call the generic Write method using reflection, picking up the execution-time type of the values that way:

  // You may well need to do more work here, if DataStream.Write is
  // overloaded.
  MethodInfo genericMethod = typeof(DataStream).GetMethod("Write");
  foreach (object value in values)
  {
      Type type = value.GetType();
      MethodInfo method = genericMethod.MakeGenericMethod(type);
      method.Invoke(dataStream, value);
  }
  

• Use dynamic typing if you’re using C# 4 and .NET 4:

  foreach (dynamic value in values)
  {
      dataStream.Write(value);
  }
  

• Explicitly check each value against your supported types:

  foreach (object value in values)
  {
      if (value is char)
      { 
          dataStream.Write((char) value);
      }
      else if (value is byte)
      {
          dataStream.Write((byte) value);
      }
      else if (value is int)
      {
          dataStream.Write((int) value);
      }
      else
      {
          throw new ArgumentException("Unsupported type in input data");
      }
  }
  

All of these are likely to be fairly slow, to be honest. The first is likely to be the slowest, but I wouldn’t like to bet on anything without testing it first.