c＃匿名类逃避内部范围块的任何方式？

Question

i want to use an anonymous class but instantiate inside a using code block and have it escape the block. is this possible?

eg, i have

using (var s = something()) {
   var instance = new { AA = s.A };
   // ... lots of code
   Console.WriteLine(instance.AA);
}

And I would rather have something like:

var instance;  // <- nope, can't do this
using (var s = something()) {
   instance = new { AA = s.A };
}
// ... lots of code
Console.WriteLine(instance.AA);

Answer 1

Easily done:

var instance = new { Name = default(string) };
using (whatever) 
{
  instance = new { Name = whatever.Whatever() };
}
...

But the better thing to do here is to create an actual class.

Or, in C# 7, consider using a tuple.

Now, if you want to get really fancy...

static R Using<A, R>(A resource, Func<A, R> body) where A : IDisposable
{
    using (resource) return body(resource);
}
...

var instance = Using(something(), s => new { AA = s.A });

But this seems silly. Just make a class!

Answer 2

I often write static Use methods for this purpose.

class SomethingDisposable : IDisposable {

   ...       

   public static T Use<T>(Func<SomethingDisposable, T> pFunc) {
      using (var somethingDisposable = new SomethingDisposable())
         return pFunc(somethingDisposable);
   }

   // also a version that takes an Action and returns nothing

   ...
}

Now you can just return whatever you want, even an anonymous type, and it'll always be safely wrapped in a using . These are very handy, for example, when working with Entity Framework.

var result = SomethingDisposable.Use(sd => sd.DoSomething());
var anonResult = SomethingDisposable.Use(sd => new { Property = sd.DoSomethingElse() });

// etc.