C# Programming/Keywords/using

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

The directive[edit]

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

Example:

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

using can also provide a namespace alias for referencing types.

Example:

using utils = Company.Application.Utilities;

The statement[edit]

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.StreamReader reader = new StreamReader("readme.txt"))
{
    // read from the file
}
 
// The file readme.txt has now been closed automatically.
 
using (Font headerFont = new Font("Arial", 12.0f),
            textFont = new Font("Times New Roman", 10.0f))
{
    // Use headerFont and textFont.
}
 
// Both font objects are closed now.



C# Keywords
abstract as base bool break
byte case catch char checked
class const continue decimal default
delegate do double else enum
event explicit extern false finally
fixed float for foreach
goto if implicit in int
interface internal is lock long
namespace new null object operator
out override params private protected
public readonly ref return sbyte
sealed short sizeof stackalloc
static string struct switch this
throw true try typeof uint
ulong unchecked unsafe ushort using
var virtual void volatile while
Special C# Identifiers
add alias get global partial
remove set value where yield