Variable declaration outside the class definition using "using" statement

Question

I have found some source code on the net and I am not able to understand this usage of using statement outside the class definition:

namespace Artfunkel
{
    using DataErrorsChangedEventManager = WeakEventManager<INotifyDataErrorInfo, DataErrorsChangedEventArgs>;

    public class DataErrorsControl : Control
    {
        private readonly Dictionary<string, CollectionContainer> _errorLookup;
      ...
    }
}

Is it possible to declare variables outside the class definition? There is no var keyword.

This source code is from https://gist.github.com/Artfunkel/868e6a88e37bd9769cd8beb04fd9837f

You may want to read the docs on that syntax: learn.microsoft.com/en-us/dotnet/csharp/language-reference/… — Camilo Terevinto
– Camilo Terevinto, Commented Oct 27, 2020 at 13:43

nathan gonzalez · Accepted Answer · 2020-10-27 13:44:18Z

1

They're basically creating an alias or alternative name for that closed generic type. Its not a variable declaration, but rather an alternative way to refer to that closed generic type, likely to prevent it from having to be typed all over the place and to make the intent more clear.

answered Oct 27, 2020 at 13:44

nathan gonzalez

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Magnetron · Accepted Answer · 2020-10-27 13:44:55Z

0

It's using using as a alias directive, to create an alias for a namespace or a type.

Read more here, it's the tird use of using: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-directive

answered Oct 27, 2020 at 13:44

Magnetron

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Paul Alan Taylor · Accepted Answer · 2020-10-27 13:51:34Z

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Just to add to some of the answers here.

using is a keyword that does multiple things in C#.

Right here, it is being used to alias one type to another name.

In its other application, it is used to force the garbage collector to get rid of the used variable at the end of the scoped block.

using (var conn = new SqlConnection("SomeConnstring"))
{
  // Things happen with conn
}

// conn is guaranteed cleaned up by GC at this point.

answered Oct 27, 2020 at 13:51

Paul Alan Taylor

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1 Comment

Lasse V. Karlsen Over a year ago

The garbage collector is not involved in IDisposable use of using. It is definitely not guaranteed to be cleaned up by GC at that point. It might be, but there is no such guarantee. This use of using only adds a call to IDisposable.Dispose() for the object at the end of the scope, it does not involve GC directly.

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