How can I replace Marshal.SizeOf(Object) with Marshal.SizeOf()?

Question

I am building a Universal class library from existing code, and I get some compiler warnings that I for the life of it cannot figure out what to do with.

I have code like this:

void SomeMethod(Object data)
{
  var size = Marshal.SizeOf(data);
  ...
}

The code builds, but in the Universal project (and, I guess, .NET 4.5.1 and higher projects) I get the following compiler warning:

warning CS0618: 'System.Runtime.InteropServices.Marshal.SizeOf(object)' is obsolete: 'SizeOf(Object) may be unavailable in future releases. Instead, use SizeOf<T>().

But how do I create a replacement for Marshal.SizeOf(Object) in the above case using the generic parameter-less method Marshal.SizeOf<T>()? Theoretically, I might not have any idea what type data is?

Is it because using Marshal.SizeOf(Object) is considered bad practice that it has been attributed Obsolete? And the take-home message should really be "refactor the code completely"?

It certainly isn't obsolete in 4.5.1. I'm guessing that it was made obsolete specifically in the Universal reference assembly because it is a pain in the neck for .NET Native ahead-of-time compiler. It is not clear why you couldn't just make SomeMethod generic. If you can't then the .NET Native toolchain is liable to have trouble as well. — Hans Passant, Oct 24 '14 at 20:57
I have removed my answer. Please see [SizeOf(T) on MSDN](http://msdn.microsoft.com/en-us/library/vstudio/dn261467(v=vs.110).aspx). It takes `` and also a parameter. You can pass your object there, and it will be measured properly. I'm pretty sure you should be able to even successfully pass `Marhal.SizeOf — quetzalcoatl, Oct 24 '14 at 21:07
Thanks for all your help, @quetzalcoatl and NemanjaBoric. Silly of me to miss that `SizeOf` overload. I will give it a try and see how well it fits my needs. — Anders Gustafsson, Oct 25 '14 at 21:30

Oliver · Answer 1 · 2014-10-29T07:37:01.973

0

Okay, after getting your comments it seems that everything you need is already there:

SizeOf<T>(T): I think this is the method you need, but you don't have to define the generic parameter explictly, due to type inference. You simple write var size = Marshal.SizeOf(myStructure); and the compiler will extract the type from the given object and fill out the generic parameter.

SizeOf<T>(): This method comes in handy when your own class is maybe already a generic class and you have a T but no real instance of the used generic type. In that case this method should be choosen.

~~How about this reflection approach:~~

private static int MySizeOf(object structure)
{
    var marshalType = typeof(Marshal);
    var genericSizeOfMethod = marshalType.GetMethod("SizeOf", Type.EmptyTypes);
    var sizeOfMethod = genericSizeOfMethod.MakeGenericMethod(structure.GetType());
    var size = (int)sizeOfMethod.Invoke(null, null);

    return size;
}

edited Oct 29 '14 at 07:37

answered Oct 28 '14 at 13:39

Oliver

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Interesting thought, although I am not entirely comfortable with introducing a reflection relying method to solve this problem. I also think your code might require some adaptation: (1) I do not think `Type.GetMethod` is available in Universal projects, you might need to traverse `TypeInfo.DeclaredMethods` to obtain the `SizeOf` overloads; (2) I think you are missing the opportunity to pass the `structure` object to the method, maybe the second argument in the `Invoke` call should be `new[] { structure }` instead of null? – Anders Gustafsson Oct 28 '14 at 13:56
Never worked with Universals, so i don't know their restrictions. For the Invoke call you don't need to pass the structure, cause we already extracted the type and used that for the generic call `Marshal.SizeOf()`. – Oliver Oct 28 '14 at 15:15
But is the unmanaged size of the `structure` object always the same? Then, why are there two `Marshal.SizeOf` overloads, `Marshal.SizeOf()` and `Marshal.SizeOf(T)`, in [the 4.5.1 and later frameworks](http://msdn.microsoft.com/en-us/library/vstudio/system.runtime.interopservices.marshal.sizeof(v=vs.110).aspx)? And, I am fairly sure that you can't do `Type.GetMethod` in a Universal project, since the method is not available for modern Windows (f.k.a. Metro) apps. – Anders Gustafsson Oct 28 '14 at 15:21
Thanks, Oliver. In principle, type inference should do the trick, yes, but it is obfuscated by overloading precedence; `Marshal.SizeOf(object)` takes precedence over `Marshal.SizeOf(T)`, which is why I get the warning message in the first place. I have not gotten to try the implications of using the `Marshal.SizeOf(T)` overload yet, but when I've done that I will report the result. – Anders Gustafsson Oct 29 '14 at 08:03

How can I replace Marshal.SizeOf(Object) with Marshal.SizeOf()?

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