C＃这个操作符类字段声明 [英] C# this operator in class field declaration

问题描述

这是一个纯粹的学术问题 - 我已经找到了getaround很轻松了。

This is a purely academic question - I have found a getaround easily enough.

在移植VB.Net类C＃中，我来到现场，其中使用this关键字作为参数在一个新的（）语句类的声明。编译器说，关键字这不是在目前情况下，可用'（VB编译器认为没有问题，这种状况）。我很容易被现场的初始化移动到类的构造器解决此得到。

While porting a VB.Net class to C#, I came upon the declaration of a field in a class which used the this keyword as a parameter in a new() statement. The compiler said the "Keyword 'this' is not available in the current context' (the VB compiler saw no problem with this state of affairs). I easily got around this by moving the field's initialization to the contructor of the class.

编辑：在阅读的意见后，我添加以下代码块

edit: after reading comments, I added the following code block

 
    public class cTransactions
    {
        private List Trans = new List();
        private List Archive = new List();
        private cDDs Debits = new cDDs(this); // complier error 
                                            //Keyword 'this' is not available in the current context
        private string path = Directory.GetCurrentDirectory() + "\";
        private bool dirty = false;
        private int LastID;
        // followed by Property declarations, ctor, methods etc.
        //...
    }
     

不过，我找不到关键字的任何引用'这个'一类的构造函数执行之前不被使用（虽然我可能已经错过了启示，在500+语言规范的页面）。这样的话，或者我应该寻找以前到外地报关行之一的一些错误？

However, I cannot find any reference to the keyword 'this' not being available before the execution of a class' constructor (though I may have missed that revelation in the 500+ pages of the language specification). Is this the case or should I be looking some error in one of the lines prior to the field declaration?

推荐答案

综观 C＃语言规范部分7.6.7：

7.6.7此访问

A 此访问的只有在一个实例
构造函数，实例方法或实例访问的块是允许的。 ...（具体略）......在比上面列出的
以外的上下文中的基本表达式的这种
中使用的是编译时错误。尤其是，它不是
可以参考这在静态方法，静态属性
访问，或在一个域声明的变量初始化。

A this-access is permitted only in the block of an instance constructor, an instance method, or an instance accessor. ... (specifics omitted) ... Use of this in a primary-expression in a context other than the ones listed above is a compile-time error. In particular, it is not possible to refer to this in a static method, a static property accessor, or in a variable-initializer of a field declaration.

因此，在上面的例子中的可变初始化使用它是一个编译时间错误。要修复它，将初始化到构造。

Therefore, using it in a variable-initializer in the example above is a compile-time error. To fix it, move the initialization into the constructor.

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