Releasing temporary COM objects

My biggest gripe would be the name, T; Add might be more illusrative of the usage. I’d also add where T : class to the generic method, but the “fluent API” seems usable. I’d also be inclined to flatten the code a bit. I can also see some ways of using the Expression API to walk an entire tree and capture all the intermediate steps, but it wouldn’t be trivial – but imagine:

using(var com = new SomeWrapper()) {
    var baz = com.Add(() => new MyComObject().Foo.Bar.Baz);
}

where that is an expression tree and we get the intermediaries automatically.

(also, you could Clear() or null the list in Dispose())

---

Like so:

static class ComExample {
    static void Main()
    {
        using (var wrapper = new ReleaseWrapper())
        {
            var baz = wrapper.Add(
                () => new Foo().Bar.Baz);
            Console.WriteLine(baz.Name);
        }
    }
}

class ReleaseWrapper : IDisposable
{
    List<object> objects = new List<object>();
    public T Add<T>(Expression<Func<T>> func)
    {
        return (T)Walk(func.Body);
    }
    object Walk(Expression expr)
    {
        object obj = WalkImpl(expr);
        if (obj != null && Marshal.IsComObject(obj) && !objects.Contains(obj)) 
        {
            objects.Add(obj);
        }
        return obj;
    }
    object[] Walk(IEnumerable<Expression> args)
    {
        if (args == null) return null;
        return args.Select(arg => Walk(arg)).ToArray();
    }
    object WalkImpl(Expression expr)
    {
        switch (expr.NodeType)
        {
            case ExpressionType.Constant:
                return ((ConstantExpression)expr).Value;
            case ExpressionType.New:
                NewExpression ne = (NewExpression)expr;
                return ne.Constructor.Invoke(Walk(ne.Arguments));
            case ExpressionType.MemberAccess:
                MemberExpression me = (MemberExpression)expr;
                object target = Walk(me.Expression);
                switch (me.Member.MemberType)
                {
                    case MemberTypes.Field:
                        return ((FieldInfo)me.Member).GetValue(target);
                    case MemberTypes.Property:
                        return ((PropertyInfo)me.Member).GetValue(target, null);
                    default:
                        throw new NotSupportedException();

                }
            case ExpressionType.Call:
                MethodCallExpression mce = (MethodCallExpression)expr;
                return mce.Method.Invoke(Walk(mce.Object), Walk(mce.Arguments));
            default:
                throw new NotSupportedException();
        }
    }
    public void Dispose()
    {
        foreach(object obj in objects) {
            Marshal.ReleaseComObject(obj);
            Debug.WriteLine("Released: " + obj);
        }
        objects.Clear();
    }
}