blocks|key|1474414|text|ByVal应该是你的“默认值”。除非您有使用ByRef的特殊原因，否则请使用它|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1474415|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

ByVal should be your "default". Use it unless you have a specific reason to use ByRef

blocks|key|1474527|text|仅当参数为"output“参数时，才使用"ByRef”。否则请使用"ByVal“。在不应显式返回值的参数上使用"ByRef“是危险的，而且很容易生成错误。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1474528|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Use "ByRef" only if the parameter is "output" parameter. Otherwise use "ByVal". Using "ByRef" on parameters which explicitly should not return values is dangerous and can easy generate bugs.

blocks|key|1689608|text|关于这一点有很多错误的信息。最重要的是你理解了difference+between+value+types+and+reference+types和difference+between+pass+by+value+and+pass+by+reference。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1689609|您几乎总是希望通过值传递。通过引用传递几乎总是为了“我想返回多个结果，而不仅仅是通过向传入的列表中添加内容”。使用按引用传递的方法的经典示例是Int32.TryParse，其中返回值是成功/失败，解析后的值由out参数“返回”。|1689610|entityMap|0|LINK|mutability|MUTABLE|url|http://pobox.com/~skeet/csharp/references.html|1|http://pobox.com/~skeet/csharp/parameters.html|2|http://msdn.microsoft.com/en-us/library/f02979c7.aspx^0|N|1E|0|22|1I|1|0|1Z|E|2|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@$A|S|B|T|1|U]|$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]]|C|$]]|$1|F|3|-4|5|6|7|12|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]|P|$5|I|J|K|C|$L|Q]]]]

There's a lot of misinformation around about this. The main thing is that you understand the <a href="http://pobox.com/~skeet/csharp/references.html" rel="noreferrer">difference between value types and reference types</a>, and the <a href="http://pobox.com/~skeet/csharp/parameters.html" rel="noreferrer">difference between pass by value and pass by reference</a>.

You almost always want to pass by value. Passing by reference is almost always for "I want to return more than one result, and not just by adding things to a list which is passed in." The classic example of a method using pass-by-reference is <a href="http://msdn.microsoft.com/en-us/library/f02979c7.aspx" rel="noreferrer">Int32.TryParse</a> where the return value is a success/failure, and the parsed value is "returned" by an out parameter.

blocks|key|1474674|text|在.net中传递对象ByVal不会复制对象，也不会消耗比ByRef更多的资源，但仍会将指针传递给函数。运行库只是确保您不能修改函数中的指针并为其返回不同的值。您仍然可以对对象内的值进行更改，并且您将在函数外部看到这些更改。这就是为什么ByRef很少被使用的原因。只有当您想要一个函数更改返回的实际对象时才需要它；因此是一个输出参数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1474675|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Passing an object ByVal in .net does not make a copy of the object and does not consume more resources then ByRef, A pointer is still passed through to the function. The runtime just ensures that you can't modify the pointer in your function and return a different value for it. You can still make changes to the values within the object and you will see those changes outside the function. That is why ByRef is uses so rarely. It is only needed when you want a function to change the actual object that is coming back; hence an output parameter.

blocks|key|1689860|text|对于所有类型，缺省值都是byValue，但是理解这两个选项对于“引用类型”(类)与值类型的含义是很重要的。(结构)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1689861|对于引用类型，如果在方法中声明引用类型变量，则该变量是方法堆栈帧中的内存位置。它不在堆上。当您初始化该变量(使用new或工厂等)时，您已经在堆上创建了一个实际的对象，并且该对象的地址存储在方法堆栈帧中声明的引用变量中。|1689862|当您将引用类型传递给另一个方法byVal时，您正在创建存储在调用方法堆栈中的地址的副本，并将该值的副本(指针地址)传递给被调用的方法，在那里它被存储在被调用方法堆栈的新内存槽中。在被调用的方法内部，新克隆的变量直接指向Heap上的同一对象。因此，使用它可以更改同一对象的属性。但您不能更改原始引用变量(在调用方法堆栈上)指向哪个堆对象。如果，在被调用的方法中我写道|1689863|++myVar+=+new+object();|code-block|syntax|javascript|1689864|调用方法中的原始变量不会更改为指向新对象。|1689865|如果我传递一个引用类型byRef，otoh，我将传递一个指向调用方法堆栈中已声明变量的指针(它包含指向堆上对象的指针)，因此它是指向对象指针的指针。它指向调用方法堆栈上的内存位置，该位置指向堆上的对象。|1689866|因此，现在，如果我更改被调用方法中变量的值，通过将其设置为一个新的object()，如上所述，因为它是调用方法中的变量的“引用”，所以我实际上是在更改调用方法中的变量所指向的对象。因此，在被调用的方法返回后，调用方法中的变量将不再指向堆上的同一原始对象。|1689867|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|U|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|V|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

The default is byValue for ALL types, but it is important to understand what the two options mean for a "reference type" (a class) as opposed to a value type. (structs).

For a reference type, if you declare a reference type variable in a method, that variable is a memory location in the stack frame of the method. It is not on the heap. When you initialize that variable (using new or a factory, whatever), then you have created an actual object on the heap, and the address of that object is stored in the declared reference variable in your methods stack frame.

When you pass a reference type to another method byVal, you are creating a copy of the address stored in the calling methods stack and passing the copy of that value (the pointer address) to the called method, where it is stored in a new memory slot in the called methods stack. Inside the called method, the new cloned variable points directly to the same object on the Heap. So using it can change the properties of the same object. But you cannot change which heap object the original reference variable (on the calling methods stack) points to. 
If, in the called method I write

<pre><code> myVar = new object();
</code></pre>

The original variable in the calling method will not have changed to point to a new object.

If I pass a reference type byRef, otoh, I am passing a pointer to the declared variable in the calling methods stack (which contains a pointer to the object on the heap) It is therefore a pointer to a pointer to the object. It points to the memory location on the calling methods stack, which points to the object on the heap. 
So now, if I change the value of the variable in the called method, by setting it to a new object(), as above, since it is a "refereence" to the variable in the calling method, I am actually changing which object the variable in the calling method is pointing to. So After the called method returns, the variable in the calling method will no longer be pointing to the same original object on the heap.

blocks|key|1689930|text|我认为永远不应该使用ByRef+--这是一种糟糕的做法。我甚至会将其应用于允许函数返回多个值(通过ByRef参数)的典型用例。函数返回包含这些多个返回值的结构化响应会更好。如果一个函数只通过其return语句返回值，这一点就会更加清晰和明显。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1689931|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I would argue that ByRef should never be used--that it's a bad practice. I would apply that even to its typical use case of allowing a function to return multiple values (via ByRef parameters). It would be better for the function to return a structured response that includes those multiple return values. It's more clear and more obvious if a function only returns values via its return statement.

blocks|key|1689949|text|Sub+last_column_process()
Dim+last_column+As+Integer

last_column+=+234
MsgBox+last_column

trying_byref+x:=last_column
MsgBox+last_column

trying_byval+v:=last_column
MsgBox+last_column

End+Sub

Sub+trying_byref(ByRef+x)
x+=+345
End+Sub

Sub+trying_byval(ByRef+v)
v+=+555
End+Sub|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1689950|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>Sub last_column_process()
Dim last_column As Integer

last_column = 234
MsgBox last_column

trying_byref x:=last_column
MsgBox last_column

trying_byval v:=last_column
MsgBox last_column

End Sub

Sub trying_byref(ByRef x)
x = 345
End Sub

Sub trying_byval(ByRef v)
v = 555
End Sub
</code></pre>

What are the things to consider when choosing between ByRef and ByVal.

I understand the difference between the two but I don't fully understand if ByRef saves resources or if we even need to worry about that in the .Net environment.

How do you decide between the two if the functionality doesn't matter in a situation?

Best Practice: ByRef or ByVal? in .Net

在ByRef和ByVal之间进行选择时，需要考虑哪些事项。我理解这两者之间的区别，但我不完全理解ByRef是否节省了资源，或者我们是否需要在.Net环境中担心这一点。如果功能在某种情况下无关紧要，你如何在两者之间做出决定？

问最佳实践: ByRef还是ByVal？在.Net中
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