Prefer Pointer than int/IntPtr

[Sunbreak]

Problem

After applying type-map with package:win32, HANDLE and HWND changed from Pointer to IntPtr

• Before

  int HidD_GetAttributes(
    HANDLE HidDeviceObject,
    PHIDD_ATTRIBUTES Attributes,
  )

typedef HANDLE = ffi.Pointer<ffi.Void>;

  HDEVINFO SetupDiGetClassDevsW(
    ffi.Pointer<GUID> ClassGuid,
    PCWSTR Enumerator,
    HWND hwndParent,
    int Flags,
  )

typedef HWND = ffi.Pointer<HWND__>;

class HWND__ extends ffi.Struct {
  @pkg_ffi.Int()
  external int unused;
}

• After

  int HidD_GetAttributes(
    int HidDeviceObject,
    PHIDD_ATTRIBUTES Attributes,
  )

  HDEVINFO SetupDiGetClassDevsW(
    ffi.Pointer<GUID> ClassGuid,
    PCWSTR Enumerator,
    int hwndParent,
    int Flags,
  )

Both before and after work. But I prefer type-safe Pointer than Int/IntPtr

Request

Could we change HANDLE and HWND to Pointer?

https://github.com/timsneath/win32/blob/4d0e4dec9bafcddef331aa96244b9d59836ce87c/lib/src/types.dart#L30

https://github.com/timsneath/win32/blob/4d0e4dec9bafcddef331aa96244b9d59836ce87c/lib/src/types.dart#L41

[timsneath]

These should be integer values though, no? They are sized to the same width as a Pointer (i.e. 64-bit on modern Windows systems, 32-bit or even 16-bit on older systems), but they are not pointers in that they don't reference a specific address in memory. You can think of them as a primary key. IntPtr seems like the right type for that, because it represents an integer which has the same size as a pointer.

(Arguably, UintPtr might be an even better fit, but we'd have to wait for Dart 2.17 for that, and in practice values are 32-bit for compatibility purposes.)

[Sunbreak]

Then why ffigen generate HANDLE and HWND as Pointer to a struct?

[timsneath]

Ah, that's a great question! The answer is that HANDLE is defined in the Windows SDK as a void *.

Here's the definition in winnt.h:

typedef void *HANDLE;
#define DECLARE_HANDLE(name) struct name##__{int unused;}; typedef struct name##__ *name

If Windows was being written today, or with a different language in mind than C, they might have done things differently. But C doesn't know whether a Pointer is being used as a reference to a memory address or just as an opaque index. You can see that there's an attempt with the DECLARE_HANDLE macro to provide some primitive typing (so for example, you can't cast a HINSTANCE to an HRGN). But fundamentally, all handles are really just pointers under the hood.

Of course, ffigen knows nothing about these semantics or higher level Windows programming abstractions like COM. That's why I haven't adopted it for win32, even though it's a great tool.

You and I are not the only ones who grapple with this - see here: microsoft/win32metadata#21

[Sunbreak]

There is a similiar question on Pointer<io_service_t> at dart-lang/native#509

Then should we use Int or IntPtr on Darwin platform?

[timsneath]

I'm sorry -- I wish I could help you with that question, but I don't know much about macOS development. Although I switch around devices a fair amount, when it comes to development, Windows is my niche!

[Sunbreak]

Thanks very much for your answer on Windows. Closing this