The attribute Obsolete is used to mark types and members of types that should no longer be used.

using System; [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Delegate | AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Event)] public class ObsoleteAttribute: Attribute { public ObsoleteAttribute() {...} public ObsoleteAttribute(string message) {...} public ObsoleteAttribute(string message, bool error) {...} public string Message { get {...} } public bool IsError{ get {...} } }

If a program uses a type or member that is decorated with the Obsolete attribute, then the compiler shall issue a warning or error in order to alert the developer, so the offending code can be fixed. Specifically, the compiler shall issue a warning if no error parameter is provided, or if the error parameter is provided and has the value false. The compiler shall issue a compile-time error if the error parameter is specified and has the value true.

[Example: In the example

[Obsolete("This class is obsolete; use class B instead")] class A { public void F() {} } class B { public void F() {} } class Test { static void Main() { A a = new A(); // warning a.F(); } }

the class A is decorated with the Obsolete attribute. Each use of A in Main results in a warning that includes the specified message, "This class is obsolete; use class B instead." end example]