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

Question

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?

Answer 1

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.