为什么属性目标'typevar“无证？ [英] Why is the attribute target 'typevar' undocumented?

问题描述

众所周知，在C＃可以指定的靶的自定义属性规范，如在实施例

As is well known, in C# one can specify the target of a custom attribute specification, as in the example

[method: SomeDecoration]
[return: SomeOtherMark]
int MyMethod();

里的指标方法：和收益帮助指定哪些因素在code中的属性属于

where the "targets" method: and return: help specify what element in the code the attribute belongs to.

根据C＃语言规范，下面的属性指标存在：

According to the C# Language Specification, the following attribute targets exist:

• 全球的：
  
  
  
  • 组装
  
  
  • 模块
  
  
  • Global ones:
    • assembly
    • module
    
    
    • 字段
    
    
    • 事件
    
    
    • 法
    
    
    • 参数
    
    
    • 属性
    
    
    • 收益
    
    
    • 键入
    
    
    • field
    • event
    • method
    • param
    • property
    • return
    • type

    他们中的一些，像字段，是的总是的多余的，因为它始终清楚什么属性坐在没有指定它们。

    Some of them, like field, are always redundant, since it is always clear what the attribute "sits" on without specifying them.

    然而，有确实存在（至少在Visual C＃中执行和版本我这里）一个附加属性的目标，即：

    However there does exist (at least in the implementation and version of Visual C# I have here) an additional attribute target, namely:

    
    
    • typevar
    
    
    • typevar

    这是允许在例如code

    which is allowed for example in the code

    class MyGenericCollection<[typevar: HereYouSee] TItem>    // legal
    {
    }
    

    属性目标 typevar ，就像字段和其他人，永远不会必需的。

    The attribute target typevar, just like field and others, is never required.

    的我的问题：的有谁知道为什么 typevar历史原因：未在说明书或文档中提到？ 2.0版本的C＃语言规范的写入时被这只是忘记了吗？或者，如果它不是一个疏忽，为什么它在所有实施？

    My question: Does anyone know the historic reason why typevar: is not mentioned in the specification or documentation? Was this simply forgotten when the 2.0 version of the C# Language Specification was written? Or if it was not an oversight, why is it implemented at all?

    推荐答案

    其实， typevar 属性目标文档，但似乎只有在规范的C＃2.0语言规范：
    的http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-334.pdf#page=399

    Actually, typevar attribute target is documented, but it seems that only in the standardized C# 2.0 Language Specification: http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-334.pdf#page=399

    无论是C＃<一个href=\"http://download.microsoft.com/download/3/8/8/388e7205-bc10-4226-b2a8-75351c669b09/CSharp%20Language%20Specification.doc\"相对=nofollow> 3.0 ，也不<一个href=\"http://download.microsoft.com/download/0/B/D/0BDA894F-2CCD-4C2C-B5A7-4EB1171962E5/CSharp%20Language%20Specification.docx\"相对=nofollow> 5.0 语言规范中提到 typevar 。 （我没有发现C＃4.0规范。）

    Neither C# 3.0, nor 5.0 Language Specification mentions typevar. (I didn't find C# 4.0 spec.)

    所以回答你的第二个问题，不，它不是遗忘在C＃2.0，但此后它遗忘:)我想，这一定是一个疏忽，因为 typevar 属性的目标仍然是（C＃5.0）有效。

    So answering your second question, no, it wasn't forgotten in C# 2.0, but it is forgotten since then :) I think this must be an oversight, since the typevar attribute target is still (C# 5.0) valid.

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