IIf（）和If之间的性能差异 [英] Performance difference between IIf() and If

问题描述

在Visual Basic中，使用 IIf 函数而不是 If 语句时是否存在性能差异？

In Visual Basic, is there a performance difference when using the IIf function instead of the If statement?

推荐答案

VB有以下如果这个问题涉及的语句，我想：

VB has the following If statement which the question refers to, I think:

' Usage 1
Dim result = If(a > 5, "World", "Hello")
' Usage 2
Dim foo = If(result, "Alternative")

第一个基本上是C＃的三元条件运算符，第二个是它的coalesce运算符（返回结果除非它是 Nothing ，在这种情况下返回替代）。 如果已取代 IIf 而后者已过时。

The first is basically C#'s ternary conditional operator and the second is its coalesce operator (return result unless it’s Nothing, in which case return "Alternative"). If has thus replaced IIf and the latter is obsolete.

就像在C＃中一样，VB的条件如果运算符短路，所以你现在可以安全地编写以下内容，这是使用 IIf function：

Like in C#, VB's conditional If operator short-circuits, so you can now safely write the following, which is not possible using the IIf function:

Dim len = If(text Is Nothing, 0, text.Length)

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