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.

The directive

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

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
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Special C# Identifiers (Contextual Keywords)
add alias async await dynamic get global nameof partial remove set value when where yield
Contextual Keywords (Used in Queries)
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