斯卡拉分配评估单元的动机是什么，而不是分配的值？ [英] What is the motivation for Scala assignment evaluating to Unit rather than the value assigned?

问题描述

Scala赋值对Unit的评价动机是什么，而不是赋值？

I / O编程中的一个常见模式是做这样的事情：< /（b）

但是在Scala中这是不可能的，因为...

  bytesRead = in.read（buffer）
  

.. returns单位，而不是bytesRead的新值。

看起来像是一个有趣的事情，可以省略函数式语言。
我想知道为什么这样做？

解决方案

我主张赋值返回赋值而不是单位。马丁和我之间来回转移，但他的观点是，为了在95％的时间内实现价值而忽略字节码并对性能产生负面影响。

What is the motivation for Scala assignment evaluating to Unit rather than the value assigned?

A common pattern in I/O programming is to do things like this:

while ((bytesRead = in.read(buffer)) != -1) { ...

But this is not possible in Scala because...

bytesRead = in.read(buffer)

.. returns Unit, not the new value of bytesRead.

Seems like an interesting thing to leave out of a functional language. I am wondering why it was done so?

解决方案

I advocated for having assignments return the value assigned rather than unit. Martin and I went back and forth on it, but his argument was that putting a value on the stack just to pop it off 95% of the time was a waste of byte-codes and have a negative impact on performance.

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