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24.3.2 Run-time retrieval of an attribut... > 24.3.2 Run-time retrieval of an attr... - Pg. 661

628 Constructor not called at compile-time CHAPTER 24: ATTRIBUTES Note in particular that the constructor C is not called during the compile-time processing of an attribute. Instead, the constructor is called at each run-time instantiation of the attribute, as detailed in §24.3.2. 24.3.2 Run-time retrieval of an attribute instance The attribute instance represented by T, C, P, and N, and associated with E can be retrieved at run- time from the assembly A using the following steps: Follow the run-time processing steps for executing an object-creation-expression of the form new T(P), using the instance constructor C and values as determined at compile- time. These steps either result in an exception, or produce an instance of T. Call this instance O. For each named-argument Arg in N, in order: Let Name be the identifier of the named-argument Arg. If Name does not identify a non-static public read-write field or property on O, then an exception is thrown. Let Value be the result of evaluating the attribute-argument-expression of Arg. If Name identifies a field on O, then set this field to the value Value. Otherwise, Name identifies a property on O. Set this property to the value Value. The result is O, an instance of the attribute class T that has been initialized with the positional-argument-listP and the named-argument-list N. [Note: The format for storing T, C, P, N (and associating it with E) in A and the mechanism to specify E and retrieve T, C, P, N from A (and hence how an attribute instance is obtained at run- time) is beyond the scope of this standard. end note] [Example: In an implementation of the CLI, the Help attribute instances in the assembly created by compiling the example program in §24.1.2 can be retrieved with the following program: using System; using System.Reflection; public sealed class InterrogateHelpUrls { public static void Main(string[] args) { Type helpType = typeof(HelpAttribute); string assemblyName = args[ 0]; foreach (Type t in Assembly.Load(assemblyName).GetTypes()) { Console.WriteLine("Type : { 0}", t.ToString()); HelpAttribute[] helpers = (HelpAttribute[])t.GetCustomAttributes(helpType, false); for (int at = 0; at != helpers.Length; at++) { Console.WriteLine("\tUrl : { 0}", helpers[ at].Url); } } } } end example]