将Dim X作为新Y与将Dim X作为Y = New Y（） [英] Dim X as New Y vs. Dim X as Y = New Y()

问题描述

重复

我不知道这一点，但有人能解释一下两者之间的区别吗？

Sad that I don't know this, but can anyone explain the difference between:

Dim X as New Y

和

Dim X as Y = New Y()

推荐答案

第一个仅推断类型为Y。第二个指定类型。这使您可以编写以下内容：

The first just infers that the type is Y. The second specifies it. This allows you to write things like:

Dim X as IList(Of String) = New List(Of String)

然后限制了使用 List（Of String）-这意味着以后您可能会选择使用 IList（Of String）的不同实现，并且仍会编译。

That then limits the scope of the choice to use List(Of String) - which means that later on you might choose to use a different implementation of IList(Of String), and it'll still compile.

当然，较短的版本确实具有简洁性的优点-如果类型名非常长（例如，使用嵌套泛型），则这很重要。对于匿名类型，您也不能表示X类型。

Of course, the shorter version does have the benefit of brevity - which can be important if you have very long type names (e.g. using nested generics). It's also required for anonymous types, where you can't express the type of X.

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