Implementing IDisposable on a sealed class

Question

I don't think this question has been asked before. I'm a bit confused on the best way to implement IDisposable on a sealed class—specifically, a sealed class that does not inherit from a base class. (That is, a "pure sealed class" which is my made up term.)

Perhaps some of you agree with me in that the guidelines for implementing IDisposable are very confusing. That said, I want to know that the way I intend to implement IDisposable is sufficient and safe.

I'm doing some P/Invoke code that allocates an IntPtr through Marshal.AllocHGlobal and naturally, I want to cleanly dispose of the unmanaged memory I've created. So I'm thinking of something like this

using System.Runtime.InteropServices;  [StructLayout(LayoutKind.Sequential)] public sealed class MemBlock : IDisposable {      IntPtr ptr;      int length;       MemBlock(int size)      {            ptr = Marshal.AllocHGlobal(size);            length = size;      }       public void Dispose()      {           if (ptr != IntPtr.Zero)           {                Marshal.FreeHGlobal(ptr);                ptr = IntPtr.Zero;                GC.SuppressFinalize(this);           }      }       ~MemBlock()      {            Dispose();      }     } 

I'm assuming that because MemBlock is completely sealed and never derives from another class that implementing a virtual protected Dispose(bool disposing) is not necessary.

Also, is the finalizer strictly necessary? All thoughts welcome.

Answer 1

The finalizer is necessary as a fallback mechanism to eventually free unmanaged resources if you forgot to call Dispose.

No, you shouldn't declare a virtual method in a sealed class. It wouldn't compile at all. Also, it's not recommended to declare new protected members in sealed classes.