Using statement in C#

using:

Using block/statement is used to free unmanaged resources.

Using statement is translated to three parts,

• Acquisition
• Usage
• Disposal

This resource is first acquired, then the usage is enclosed in a try statement with a finally clause. The object then gets disposed in the finally clause.

using (MemoryStream objStream = new MemoryStream())
{
    objStream.WriteTo(Response.OutputStream);
}

this code gets translated to

MemoryStream objStream = new MemoryStream();
try
{
    objStream.WriteTo(Response.OutputStream);
}
finally
{
    if(objStream !=null)
       ((IDisposable)objStream).Dispose();
}

Objects that implement IDisposable can be used in a using statement. Calling Dispose() explicitly (or implicitly via a using statement) can have performance benefits.

"Code that is using a resource can call Dispose() to indicate that the resource is no longer needed. If Dispose() is not called, then automatic disposal eventually occurs as a consequence of garbage collection." - MSDN

In the below code we can observe the following points,

• If we use using block along a Customer type, it give a compiler error, saying that "type used in a using statement must be implicitly convertible to 'System.IDisposable'".
• Same if use with Student type, it does not give any error, because it implements System.IDisposable interface.

Sample code -