ComPtr<T> improvements, new __uuidof<T> macro

sources/Interop/Windows/shared/uuids/Windows.Manual.cs

@@ -0,0 +1,81 @@
+// Copyright © Tanner Gooding and Contributors. Licensed under the MIT License (MIT). See License.md in the repository root for more information.
+
+// Ported from shared/uuids.h in the Windows SDK for Windows 10.0.19041.0
+// Original source is Copyright © Microsoft. All rights reserved.
+
+using System;
+using System.ComponentModel;
+using System.Runtime.CompilerServices;
+
+namespace TerraFX.Interop
+{
+    public static partial class Windows
+    {
+        /// <summary>Retrieves the GUID of of a specified type.</summary>
+        /// <typeparam name="T">The type to retrieve the GUID for.</typeparam>
+        /// <returns>A <see cref="UuidOfType"/> value wrapping a pointer to the GUID data for the input type. This value can be either converted to a <see cref="Guid"/> pointer, or implicitly assigned to a <see cref="Guid"/> value.</returns>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static unsafe UuidOfType __uuidof<T>()
+            where T : unmanaged
+        {
+            return new UuidOfType(UUID<T>.RIID);
+        }
+
+        /// <summary>
+        /// A proxy type that wraps a pointer to GUID data. Values of this type can be implicitly
+        /// converted to and assigned to <see cref="Guid"/>* or <see cref="Guid"/> parameters.
+        /// </summary>
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public readonly unsafe ref struct UuidOfType
+        {
+            private readonly Guid* riid;
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            internal UuidOfType(Guid* riid)
+            {
+                this.riid = riid;
+            }
+
+            /// <summary>
+            /// Reads a <see cref="Guid"/> value from the GUID buffer for a given <see cref="UuidOfType"/> instance.
+            /// </summary>
+            /// <param name="guid">The input <see cref="UuidOfType"/> instance to read data for.</param>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public static implicit operator Guid(UuidOfType guid) => *guid.riid;
+
+            /// <summary>
+            /// Returns the <see cref="Guid"/>* pointer to the GUID buffer for a given <see cref="UuidOfType"/> instance.
+            /// </summary>
+            /// <param name="guid">The input <see cref="UuidOfType"/> instance to read data for.</param>
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public static implicit operator Guid*(UuidOfType guid) => guid.riid;
+        }
+
+        /// <summary>
+        /// A helper type to provide static GUID buffers for specific types.
+        /// </summary>
+        /// <typeparam name="T">The type to allocate a GUID buffer for.</typeparam>
+        private static unsafe class UUID<T>
+            where T : unmanaged
+        {
+            /// <summary>
+            /// The pointer to the <see cref="Guid"/> value for the current type.
+            /// </summary>
+            /// <remarks>The target memory area should never be written to.</remarks>
+            public static readonly Guid* RIID = CreateRIID();
+
+            /// <summary>
+            /// Allocates memory for a <see cref="Guid"/> value and initializes it.
+            /// </summary>
+            /// <returns>A pointer to memory holding the <see cref="Guid"/> value for the current type.</returns>
+            private static Guid* CreateRIID()
+            {
+                Guid* p = (Guid*)RuntimeHelpers.AllocateTypeAssociatedMemory(typeof(T), sizeof(Guid));
+
+                *p = typeof(T).GUID;
+
+                return p;
+            }
+        }
+    }
+}