c# - C# 中的 System.AttributeTargets.GenericParameter：如何使用这样的属性？

Question

在 C# 中，当指定应该如何使用属性类时，枚举中有一个GenericParameter值。System.AttributeTargets我们如何应用这样的属性，语法是什么？

[System.AttributeUsage(System.AttributeTargets
public sealed class MyAnnotationAttribute : System.Attribute {
    public string Param { get; private set; }
    public MyAnnotationAttribute(string param) { Param = param; }
}

同样的问题也适用于其他奇异的属性目标，例如System.AttributeTargets.Module（我什至不知道如何声明主模块以外的模块？？？），System.AttributeTargets.Parameter以及System.AttributeTargets.ReturnValue.

Answer 1

// Assembly and module
[assembly: AttributesTest.MyAnnotation("Assembly")]

[module: AttributesTest.MyAnnotation("Module")]

namespace AttributesTest
{
    // The attribute
    [System.AttributeUsage(System.AttributeTargets.All, AllowMultiple = true)]
    public sealed class MyAnnotationAttribute : System.Attribute
    {
        public string Param { get; private set; }
        public MyAnnotationAttribute(string param) { Param = param; }
    }

    // Types
    [MyAnnotation("Class")]
    public class SomeClass { }

    [MyAnnotation("Delegate")]
    public delegate int SomeDelegate(string s, float f);

    [MyAnnotation("Enum")]
    public enum SomeEnum { ValueOne, ValueTwo }

    [MyAnnotation("Interface")]
    public interface SomeInterface { }

    [MyAnnotation("Struct")]
    public struct SomeStruct { }

    // Members
    public class MethodsExample
    {
        [MyAnnotation("Constructor")]
        public MethodsExample() { }

        [MyAnnotation("Method")]
        public int SomeMethod(short s) { return 42 + s; }

        [MyAnnotation("Field")]
        private int _someField;

        [MyAnnotation("Property")]
        public int SomeProperty {
            [MyAnnotation("Method")] get { return _someField; }
            [MyAnnotation("Method")] set { _someField = value; }
        }

        private SomeDelegate _backingField;

        [MyAnnotation("Event")]
        public event SomeDelegate SomeEvent {
            [MyAnnotation("Method")] add { _backingField += value; }
            [MyAnnotation("Method")] remove { _backingField -= value; }
        }
    }

    // Parameters
    public class ParametersExample<T1, [MyAnnotation("GenericParameter")]T2, T3>
    {
        public int SomeMethod([MyAnnotation("Parameter")]short s) { return 42 + s; }
    }

    // Return value
    public class ReturnValueExample
    {
        [return: MyAnnotation("ReturnValue")]
        public int SomeMethod(short s) {
            return 42 + s;
        }
    }
}