C# – Disposable Using Pattern

  using (FileStream fileStream = new FileStream(path))
  {
    // do something
  }

Now I know the using pattern is an implementation of IDisposable, namely that a Try/Catch/Finally is set up and Dispose is called on the object. My question is how the Close method is handled.

MSDN says that it is not called, but I have read otherwise.

I know that the FileStream inherrits from Stream which is explained here. Now that says not to override Close() because it is called by Dispose().

So do some classes just call Close() in their Dispose() methods or does the using call Close()?

Best Answer

The using statement only knows about Dispose(), but Stream.Dispose calls Close(), as documented in MSDN:

Note that because of backward compatibility requirements, this method's implementation differs from the recommended guidance for the Dispose pattern. This method calls Close, which then calls Stream.Dispose(Boolean).

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

C# – the best workaround for the WCF client `using` block issue

Actually, although I blogged (see Luke's answer), I think this is better than my IDisposable wrapper. Typical code:

Service<IOrderService>.Use(orderService=>
{
  orderService.PlaceOrder(request);
});

(edit per comments)

Since Use returns void, the easiest way to handle return values is via a captured variable:

int newOrderId = 0; // need a value for definite assignment
Service<IOrderService>.Use(orderService=>
  {
    newOrderId = orderService.PlaceOrder(request);
  });
Console.WriteLine(newOrderId); // should be updated

Best Answer

Related Solutions

C# – Should ‘using’ directives be inside or outside the namespace

C# – the best workaround for the WCF client `using` block issue

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