在Scala中，为什么模式匹配未拾取NaN? [英] In Scala, why is NaN not being picked up by pattern matching?

问题描述

我的方法如下

  def myMethod(myDouble: Double): Double = myDouble match {
    case Double.NaN => ...
    case _ => ...
  }

IntelliJ调试器显示NaN，但是在我的模式匹配中没有发现.有没有可能我忽略的情况

The IntelliJ debugger is showing NaN but this is not being picked up in my pattern matching. Are there possible cases I am omitting

推荐答案

这是一个通用规则，如何根据IEEE 754比较64位浮点数(与Scala甚至与Java无关，请参见

It is a general rule how 64-bit floating point numbers are compared according to IEEE 754 (not Scala or even Java related, see NaN):

double n1 = Double.NaN;
double n2 = Double.NaN;
System.out.println(n1 == n2);     //false

这个想法是NaN是 unknown 或 indeterminate 的标记值.比较两个未知值应该总是产生false，因为它们很好...未知.

The idea is that NaN is a marker value for unknown or indeterminate. Comparing two unknown values should always yields false as they are well... unknown.

如果要与NaN一起使用模式匹配，请尝试以下操作:

If you want to use pattern matching with NaN, try this:

myDouble match {
    case x if x.isNaN => ...
    case _ => ...
}

但是我认为模式匹配将使用严格的双重比较，因此请谨慎使用此构造.

But I think pattern matching will use strict double comparison so be careful with this construct.

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