C＃外部参数
下面两个代码片段有什么区别？
public void foo(out classA x)
{
y = new classA();
x = y;
}
第二个：
public void foo(out classA x)
{
classA y;
x = y;
}
第二个片段是否危险，因为 x 现在拥有对此本地 y 的引用，该引用在退出 foo 后可能已经死亡？
为什么我们一般都要用“新”？
我有点困惑，因为在 C++ 中，如果第二个片段中的 x 是一个指针，则语句 x = y 甚至不会编译，因为 y 不是指针。
What is the difference between the following two code snippets?
public void foo(out classA x)
{
y = new classA();
x = y;
}
and the second:
public void foo(out classA x)
{
classA y;
x = y;
}
Is it true that the second snippet is dangerous, because x has now a reference to this local y, which might be already dead after exiting foo?
Why do we have to use "new" in general?
I'm a bit confused, because in C++, if x in the second snippet would be a pointer, the statement x = y would not even compile since y is not a pointer.
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让我们暂时假设第二个片段是
片段，因为您写的它根本不会在C＃中编译。
y必须先分配。行clasta y;不会像在C ++中那样在堆栈上创建clasta的实例。它只是声明类型clasta的变量y。考虑到编译片段，将
out变量分配给本地声明的变量，并且初始化的对象在任何方面都不是危险的。classay指向并分配给x的对象将保持活力，直到x熄灭范围的范围在何处/使用/使用。Let's assume for a moment that the second snippet is
The snippet as you wrote it does not compile in C# at all.
yhas to be assigned first. The lineclassA y;does not create an instance ofclassAon the stack as it would in C++. It simply declares a variableyof typeclassA.With the compiling snippet in mind, assigning an
outvariable to a locally declared and initialized object is not dangerous in any way. TheclassAobject thatypoints to and that is assigned toxwill remain alive and well untilxgoes out of scope wherever it's declared/used.我认为您的困惑在于，在 C++ 中，第二个示例将返回对堆栈分配对象的引用。在 C# 中不会发生这种情况。
给出 C# 中的第二个示例：
无论如何，这可能无法编译，因为
y从未分配过值。Your confusion, I think, is that in C++ the second example would return a reference to a stack-allocated object. That doesn't happen in C#.
Given your second example in C#:
This probably won't compile, anyway, because
yis never assigned a value.不在 C# 中；您正在考虑像 C 或 C++ 这样的本地语言，它们允许使用指向局部变量的指针。在 C# 中，一切（在合理范围内）都是对托管对象的引用。一切本质上都在堆上。
Not in C#; you're thinking of native languages like C or C++ that allow one to take a pointer to a local variable. In C#, everything (within reason) is a reference to a managed object. Everything is essentially on the heap.
这并不危险，因为除非在方法返回或退出之前给出所有“out”参数的定义，否则代码将无法编译。
It is not dangerous because the code will NOT be able to be compiled unless all "out" parameters are given a definition before the method returns or exits.