C# Programming/Keywords/using

The using keyword has two completely unrelated meanings in C#, depending on if it is used as a directive or a statement.

using as a directive resolves unqualified type references so that a developer doesn't have to specify the complete namespace.

Example:

usingSystem;

// A developer can now type ''Console.WriteLine();'' rather than ''System.Console.WriteLine()''.

using can also provide a namespace alias for referencing types.

Example:

usingutils=Company.Application.Utilities;

using as a statement automatically calls the dispose on the specified object. The object must implement the IDisposable interface. It is possible to use several objects in one statement as long as they are of the same type.

Example:

using(System.IO.StreamReaderreader=newStreamReader("readme.txt"))
{
// read from the file
}

// The file readme.txt has now been closed automatically.
using(FontheaderFont=newFont("Arial",12.0f),
textFont=newFont("Times New Roman",10.0f))
{
// Use headerFont and textFont.
}
// Both font objects are closed now.

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