How can you know whether a parameter or return type is a handle type?

[revosw]

Handles are merely pointers to objects. The size of handles are therefore dependent on the platform - 32 bit on 32 bit machines and 64 bit on 64 bit machines.

Take for example MSIHANDLE.

.class public sequential ansi sealed beforefieldinit Windows.Win32.System.ApplicationInstallationAndServicing.MSIHANDLE
	extends [netstandard]System.ValueType
{
	.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.RAIIFreeAttribute::.ctor(string) = (
		01 00 0e 4d 73 69 43 6c 6f 73 65 48 61 6e 64 6c
		65 00 00
	)
	.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.InvalidHandleValueAttribute::.ctor(int64) = (
		01 00 ff ff ff ff ff ff ff ff 00 00
	)
	.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.InvalidHandleValueAttribute::.ctor(int64) = (
		01 00 00 00 00 00 00 00 00 00 00 00
	)
	.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.NativeTypedefAttribute::.ctor() = (
		01 00 00 00
	)
	// Fields
	.field public uint32 Value

} // end of class Windows.Win32.System.ApplicationInstallationAndServicing.MSIHANDLE

Alright, so we see that there's an InvalidHandleValueAttribute on it, which is quite revealing that it's a handle. The RAIIFreeAttribute also strongly hints that it's a handle, since we can release it with a separate function. But it's a uint32, which forces the handle size to be 32 bits on 64-bit platforms.

What about HWND?

.class public sequential ansi sealed beforefieldinit Windows.Win32.Foundation.HWND
	extends [netstandard]System.ValueType
{
	.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.AlsoUsableForAttribute::.ctor(string) = (
		01 00 06 48 41 4e 44 4c 45 00 00
	)
	.custom instance void [Windows.Win32.winmd]Windows.Win32.Foundation.Metadata.NativeTypedefAttribute::.ctor() = (
		01 00 00 00
	)
	// Fields
	.field public void* Value

} // end of class Windows.Win32.Foundation.HWND

Doesn't seem to have any of the two attributes like MSIHANDLE does. It does, however, have a void* type, which is great, since that's what I ultimately want to insert in the projection.

There are a lot of handle types, and it will be error prone to try to list them all. I appreciate all guidance on this.

[Ekopalypse]

Handles are merely pointers to objects. The size of handles are therefore dependent on the platform - 32 bit on 32 bit machines and 64 bit on 64 bit machines.

This is a wrong assumption, because as you have noticed, there are handles that have fixed sizes of integers, like MSIHANDLE.

From msi.h

typedef unsigned long MSIHANDLE; 

Trust the source Luke :-D

[revosw]

I think I'm too stuck on the idea that handles point to objects. After some reading, I'm getting that handles don't really point to anything in memory directly. According to this stack overflow post, handles are just some index into an internal table. By giving the handle a type, you can ensure that you don't pass a handle of one type into a function that expects a handle of another type.
https://stackoverflow.com/a/39602020

Thanks for the tip that eventually cleared the confusion!