Vanara/Core/InteropServices/ComReleaser.cs

using System;
using System.Runtime.InteropServices;

namespace Vanara.InteropServices
{
	/// <summary>A safe variable to hold an instance of a COM class that automatically calls <see cref="Marshal.ReleaseComObject(object)"/> on disposal.</summary>
	/// <typeparam name="T">The type of the COM object.</typeparam>
	/// <seealso cref="System.IDisposable"/>
	public class ComReleaser<T> : IDisposable where T : class
	{
		/// <summary>Initializes a new instance of the <see cref="ComReleaser{T}"/> class.</summary>
		/// <param name="obj">The COM object instance.</param>
		/// <exception cref="ArgumentNullException">obj</exception>
		/// <exception cref="ArgumentException">Argument value must be a COM object. - obj</exception>
		public ComReleaser(T obj)
		{
			if (obj == null) throw new ArgumentNullException("obj");
			if (!obj.GetType().IsCOMObject) throw new ArgumentException("Argument value must be a COM object.", nameof(obj));
			Item = obj;
		}

		/// <summary>Gets the COM object.</summary>
		/// <value>The COM object.</value>
		public T Item { get; private set; }

		/// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
		public void Dispose()
		{
			if (Item == null) return;
			Marshal.FinalReleaseComObject(Item);
			Item = null;
		}

		/// <summary>Performs an implicit conversion from <see cref="ComReleaser{T}"/> to <see cref="T"/>.</summary>
		/// <param name="co">The <see cref="ComReleaser{T}"/> instance.</param>
		/// <returns>The result of the conversion.</returns>
		public static implicit operator T(ComReleaser<T> co) => co.Item;
	}
}