PointerToolkit 1.0.0-preview5

PointerToolkit

Provides structs that wrap pointers, as well as Unsafe, Interlocked, and Volatile operations on ref pointers.

All of the functionality contained within is being used for the work in my upcoming Paint.NET v4.4 release. I'm porting 50,000 lines of C++/CLI, almost all classes that wrap native COM objects, to C#. This package, along with TerraFX.Interop.Windows, are the foundation for this work.

The Ptr and Ptr<T> structs are straightforward enough, they simply wrap a pointer and provide all the casting operators you will need. Pointers up to 3 levels of indirection are supported, e.g. void*** and T***, viaPtrPtr and PtrPtrPtr and their generic versions.

The UnsafePtr, InterlockedPtr, and VolatilePtr classes provided methods similar to what is available with Unsafe, Interlocked, and Volatile, except that they work on ref pointers (ref void*, ref T*, as well as ** and *** variants). Refs to pointers are otherwise impossible to work well with in C# without these methods. You can't break them out of their "jail"; refs to pointers just don't work with generics or other attempted tricks employing combinations of &, *, ref, in, Unsafe, etc.

public static unsafe class UnsafePtr
{
    public static ref T As<T>(ref void* source) where T : unmanaged;
    public static ref U As<T, U>(ref T* source) where T : unmanaged where U : unmanaged;
    // etc.
}

public static unsafe class InterlockedPtr
{
    public static void* Exchange(ref void* location1, void* value);
    public static T* Exchange<T>(ref T* location1, T* value) where T : unmanaged;
    // etc.
}

public static unsafe class VolatilePtr
{
    public static void* Read(ref void* location);
    public static T* Read<T>(ref T* location) where T : unmanaged;
    public static void Write(ref void* location, void* value);
    public static void Write<T>(ref T* location, T* value) where T : unmanaged;

    // etc.
}

These structs are supported by the PtrOperators class, which contains __ptr() methods meant to be used in conjunction with a global using static PointerToolkit.PtrOperators; statement. They make it easy to pass pointers into places where they normally can't be used, such as in generics and generic delegates. The name __ptr() was chosen to be similar to vendor-specific additions in various C++ compilers, such as how Microsoft has __uuidof() for working with COM interface identifiers.

For instance, let's say you want to call a method on a COM object inside the delegate passed to String.Create(). Without PointerToolkit or your own struct wrappers, you'd have to pass it in as an IntPtr and cast it back yourself because you can't specify a pointer type for the T in SpanAction<T> . Ptr<IFoo> helps with that. In addition, the __ptr() "operator methods" help reduce the typing and duplication of types even further:

(an example from my wrapper for Direct2D's ID2D1Properties)

public string? TryGetPropertyName(int index)
{
    using var @lock = EnterFactoryLock();

    uint dwNameLength = this.pD2D1Properties->GetPropertyNameLength(unchecked((uint)index));
    if (dwNameLength == 0)
    {
        return null;
    }

    return string.Create(
        checked((int)dwNameLength),        
        // without __ptr(), I'd have to type (Ptr<ID2D1Properties>)
        (__ptr(this.pD2D1Properties), index), 
        static (Span<char> dst, (Ptr<ID2D1Properties> pD2D1Properties, int index) e) =>
        {
            fixed (char* pDst = dst)
            {
                HRESULT hr = e.pD2D1Properties.Get()->GetPropertyName(
                    unchecked((uint)e.index),
                    (ushort*)pDst,
                    (uint)(dst.Length + 1));

                hr.ThrowOnError();
            }
        });
}

CastPtr<...> is also provided, which can be used to generate static __cast() "method operators." This solves the problem where you have (e.g.) an ID2D1SolidColorBrush* that you need to pass to a method that takes a pointer to a base interface, such as ID2D1Brush* or even IUnknown*. C# does not have struct inheritance, so all of the COM interface structs in TerraFX.Interop.Windows are unrelated as far as it can tell.

Instead of forcing a pointer cast with (ID2D1Brush*), which denies the compiler a chance to verify that the cast is safe, you can use __cast(p) (along with an appropriate using static declaration). A temporary CastPtr<ID2D1SolidColorBrush, ID2D1Brush, ID2D1Resource, IUnknown> will be created which will implicitly cast to pointers of all of those base interface pointer types. (Note that "interface" in this case refers to a COM interface, not a managed interface.) The generation of these __cast() operators is not yet provided by this package, but is currently prototyped in the Paint.NET codebase to help with my use of TerraFX.Interop.Windows.