通过引用传递与返回类实例

发布于 2024-12-20 16:09:25 字数 366 浏览 2 评论 0 原文

根据标题，将引用类型传递给方法有什么区别，例如：

public void GetStream(Stream outputStream)
{
   outputStream.Write(data);
}

public Stream GetStream()
{
   MemoryStream ms = new MemoryStream();
   ms.Write(data);
   return ms; 
}

我注意到很多 Java 代码通过引用传递类（不确定其确切原因）。然而在 .NET 中这只是一个偏好问题吗？

你什么时候会选择其中之一而不是另一个？

原文

As per title is there any difference passing a reference type to a method such as:

public void GetStream(Stream outputStream)
{
   outputStream.Write(data);
}

public Stream GetStream()
{
   MemoryStream ms = new MemoryStream();
   ms.Write(data);
   return ms; 
}

I noticed alot of Java code passes class by reference (not sure of the exact reasons for this). However in .NET is this just a matter of preference?

When would you choose one over the other?

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_蜘蛛 2024-12-27 16:09:25

两者非常不同。在您的第一个示例中，调用者负责创建一个流（他们喜欢的任何类型），并且可以传递已经位于某个任意位置的流。

在第二个例子中，被调用者已经确定了流的类型，并且始终在位置 0 处写入。

如果您的第一个示例是相反：

public void GetStream(out stream outputStream)
{
   outputStream = new MemoryStream();
   outputStream.Write(data);
}

它们至少会更接近可比较。

在这里，主要区别在于调用者必须有一个声明的变量来捕获outputStream，而在其他情况下，调用者可以忽略返回的流值。

然而，第二种形式（返回值）更常见 - 如果一个方法有一个返回值，那么最好是该方法返回该值，而不是一个 out 参数的 >void 方法 - 大多数情况下，在 .NET 中，应该谨慎使用 out 参数（并且仅当该方法的返回值已经是有用的东西）。此类方法的一个示例是各种类型的 TryParse 方法，该方法返回 bool （表示成功），并且解析的值作为 传回输出参数。

The two are very different. In your first example, the caller is responsible for creating a stream (of whatever kind they prefer), and may pass a stream that is already positioned at some arbitrary position.

In the second, the callee has determined the type of stream, and is always writing at position 0.

If your first example was instead:

public void GetStream(out stream outputStream)
{
   outputStream = new MemoryStream();
   outputStream.Write(data);
}

they would at least be closer to comparable.

Here, the major difference is that the caller has to have a declared variable to capture the outputStream, whereas in the other case, the caller could ignore the returned stream value.

However, the second from (returning the value) is more commonly seen - if a method has a single value to return, it's by far preferred that that value is returned by the method, rather than a void method with an out parameter - mostly, in .NET, out parameters should be used sparingly (and only if the return value from the method is already something useful). An example of such a method would be the TryParse methods on various types, that return a bool (indicating success), and the parsed value is passed back as an out parameter.