问题描述

C# 属性如何可能在其名称中包含Attribute"(例如 DataMemberAttribute)但在没有此后缀的情况下进行了初始化?例如:

[DataMember]私人诠释我；

根据C# 语言规范,

按照惯例，属性类以Attribute 后缀命名.type-name 形式的 attribute-name 可以包含或省略此后缀.

这是 C# 编译器提供的快捷方式，绝不是 CLR 功能.编译器对属性进行特殊处理的另一个示例是 ObsoleteAttribute属性:此属性强制编译器发出警告/错误，但它对 CLR 没有特殊意义.

至于属性是如何解析的，请看上面的链接.总结一下:

如果找到带有和不带有此后缀的属性类，则存在歧义，并导致编译时错误.如果 attribute-name 的拼写使得其最右边的标识符是 逐字标识，则只匹配不带后缀的属性，从而解决这种歧义.

逐字标识符"是带有 @ 前缀的标识符.

继续使用 MSDN:

使用系统；[AttributeUsage(AttributeTargets.All)]公共类 X:属性{}[AttributeUsage(AttributeTargets.All)]公共类XAttribute:属性{}[X]//错误:歧义类 Class1 {}[XAttribute]//指 XAttribute类 Class2 {}[@X]//指 X类 Class3 {}[@XAttribute]//指 XAttribute类 Class4 {}

<块引用>

属性 [X] 不明确，因为它可以引用 X 或 XAttribute.使用逐字标识符允许在这种罕见的情况下指定确切的意图.属性 [XAttribute] 没有歧义(尽管如果有一个名为 XAttributeAttribute 的属性类就会有歧义！).如果删除了类 X 的声明，则两个属性都引用名为 XAttribute 的属性类，如下所示:

使用系统；[AttributeUsage(AttributeTargets.All)]公共类XAttribute:属性{}[X]//指 XAttribute类 Class1 {}[XAttribute]//指 XAttribute类 Class2 {}[@X]//错误:没有名为X"的属性类 Class3 {}

How is it possible that C# attributes have "Attribute" in their name (e.g. DataMemberAttribute) but are initialized without this suffix? e.g.:

[DataMember]
private int i;

According to the C# Language Specification,

By convention, attribute classes are named with a suffix of Attribute. An attribute-name of the form type-name may either include or omit this suffix.

This is a shortcut provided by the C# compiler and by no means a CLR feature. Another example of special treatment of attributes by the compiler is an ObsoleteAttribute attribute: this one forces a compiler to issue a warning/error, but it has no special meaning for the CLR.

As for how attributes are resolved, see the link above. To sum it up:

If an attribute class is found both with and without this suffix, an ambiguity is present, and a compile-time error results. If the attribute-name is spelled such that its right-most identifier is a verbatim identifier, then only an attribute without a suffix is matched, thus enabling such an ambiguity to be resolved.

A "verbatim identifier" is an identifier with an @ prefix.

Continuing with MSDN:

using System;

[AttributeUsage(AttributeTargets.All)]
public class X: Attribute
{}

[AttributeUsage(AttributeTargets.All)]
public class XAttribute: Attribute
{}

[X]                  // Error: ambiguity
class Class1 {}

[XAttribute]         // Refers to XAttribute
class Class2 {}

[@X]                  // Refers to X
class Class3 {}

[@XAttribute]         // Refers to XAttribute
class Class4 {}

The attribute [X] is ambiguous, since it could refer to either X or XAttribute. Using a verbatim identifier allows the exact intent to be specified in such rare cases. The attribute [XAttribute] is not ambiguous (although it would be if there was an attribute class named XAttributeAttribute!). If the declaration for class X is removed, then both attributes refer to the attribute class named XAttribute, as follows:

using System;
[AttributeUsage(AttributeTargets.All)]
public class XAttribute: Attribute
{}

[X]                  // Refers to XAttribute
class Class1 {}

[XAttribute]         // Refers to XAttribute
class Class2 {}

[@X]                  // Error: no attribute named "X"
class Class3 {}

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