为什么C＃不传递财产作为参考提供内部帮手？ [英] why C# does not provide internal helper for passing property as reference?

问题描述

直到你看了整个帖子，请不要回答的问题！谢谢你。

Please do not answer to the question until you read entire post! Thank you.

对于所有在C＃中现有的（如lambda表达式，或自动属性）的助手是很奇怪的，我说我不能被引用传递属性。比方说，我想做到这一点：

With all helpers existing in C# (like lambdas, or automatic properties) it is very odd for me that I cannot pass property by a reference. Let's say I would like to do that:

foo(ref my_class.prop);

我得到的错误，所以我写来代替：

I get error so I write instead:

{
   var tmp = my_class.prop;
   foo(tmp);
   my_class.prop = tmp;
}

和现在的作品。但是，请注意两件事情：

And now it works. But please notice two things:

1. 这是通用模板，我没有把任何地方的类型，只有无功，所以它适用于财产所有类型和号码，我必须要通过

1. it is general template, I didn't put anywhere type, only "var", so it applies for all types and number of properties I have to pass

我必须这样做一遍又一遍，没有好处 - 它是机械的工作

I have to do it over and over again, with no benefit -- it is mechanical work

存在的问题居然杀死这类有用的功能交换。互换通常是3线长，但由于它需要2引用，称它需要5行。当然，这是胡说八道，我只是写我每次想叫它交换的手。但是，这显示了C＃防止可重用的代码，坏

The existing problem actually kills such useful functions as Swap. Swap is normally 3 lines long, but since it takes 2 references, calling it takes 5 lines. Of course it is nonsense and I simply write "swap" by hand each time I would like to call it. But this shows C# prevents reusable code, bad.

那么 - 有什么不好的可能发生，如果编译器会自动创建临时变量（如我做手工），调用函数，并分配值回属性？这是在任何危险吗？我没有看到它，所以我很好奇你怎么想，为什么这个问题的设计看起来像它现在看起来。

So -- what bad could happen if compiler automatically create temporary variables (as I do by hand), call the function, and assign the values back to properties? Is this any danger in it? I don't see it so I am curious what do you think why the design of this issue looks like it looks now.

干杯，

修改作为280Z28放弃对性能我还是觉得用临时变量包装性能将是有益的跳动自动ref包装的理念很好的例子。也许是这样的：

EDIT As 280Z28 gave great examples for beating idea of automatically wrapping ref for properties I still think wrapping properties with temporary variables would be useful. Maybe something like this:

Swap(inout my_class.prop1,inout my_class.prop2);

否则，对于C＃没有真正的交换： - （

Otherwise no real Swap for C# :-(

推荐答案

有很多假设，你可以对意义和 REF的行为参数，例如：

There are a lot of assumptions you can make about the meaning and behavior of a ref parameter. For example,

案例1：

int x;
Interlocked.Increment(ref x);

如果您可以通过文献传递一个属性，以这种方法，调用会相同的，但它会的完全的打败方法的语义

If you could pass a property by ref to this method, the call would be the same but it would completely defeat the semantics of the method.

案例2：

void WaitForCompletion(ref bool trigger)
{
    while (!trigger)
        Thread.Sleep(1000);
}

摘要：由-ref参数传递一个内存位置函数的地址的一种实现创建。以按引用传递属性将是语义上等同于价值，这恰恰是你不允许的行为时，你的参数 REF 之一。

Summary: A by-ref parameter passes the address of a memory location to the function. An implementation creating a temporary variable in order to "pass a property by reference" would be semantically equivalent to passing by value, which is precisely the behavior that you're disallowing when you make the parameter a ref one.

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