Get to know Attributes - CSharp Custom Type

Introduction

An attribute is defined by a class that inherits from the abstract class System.Attribute.

To attach an attribute to a code element, specify the attribute's type name in square brackets, before the code element.

The following attaches the ObsoleteAttribute to the Foo class:

[ObsoleteAttribute]
public class Foo {...}

C# allows you to omit the suffix when attaching an attribute:

[Obsolete]
public class Foo {...}

ObsoleteAttribute is a type declared in the System namespace:

public sealed class ObsoleteAttribute : Attribute {...}