What is the C# Using block and why should I use it?

Issue

What is the purpose of the Using block in C#? How is it different from a local variable?

Solution

If the type implements IDisposable, it automatically disposes that type.

Given:

public class SomeDisposableType : IDisposable
{
   ...implmentation details...
}

These are equivalent:

SomeDisposableType t = new SomeDisposableType();
try {
    OperateOnType(t);
}
finally {
    if (t != null) {
        ((IDisposable)t).Dispose();
    }
}
using (SomeDisposableType u = new SomeDisposableType()) {
    OperateOnType(u);
}

The second is easier to read and maintain.


Since C# 8 there is a new syntax for using that may make for more readable code:

using var x = new SomeDisposableType();

It doesn’t have a { } block of its own and the scope of the using is from the point of declaration to the end of the block it is declared in. It means you can avoid stuff like:

string x = null;
using(var someReader = ...)
{
  x = someReader.Read();
}

And have this:

using var someReader = ...;
string x = someReader.Read();

Answered By – plinth

Answer Checked By – Willingham (AngularFixing Volunteer)

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