scala: using function definitions

Question

In the code below, the first function compiles. The second doesn't compile.

type FTDoubleDouble_Double = (Double, Double) => Double
val _dividedBy: FTDoubleDouble_Double =
{
    _ / _.toDouble
}
val _dividedByThenLog: FTDoubleDouble_Double =
{
    val result1 =  _ / _.toDouble
    scala.math.log(result1)
}

The compilation error is

cannot resolve symbol /

I am sure this is basic, but I am a bit confused.

can you please look into this:alvinalexander.com/scala/…

Raman Mishra
– Raman Mishra

2018-09-19 07:10:43 +00:00
Commented Sep 19, 2018 at 7:10 — Raman Mishra
– Raman Mishra, Commented Sep 19, 2018 at 7:10

jwvh · Accepted Answer · 2018-09-19 07:56:32Z

3

In the 1st case the type ascription helps the compiler figure out what the underscores are supposed to represent: 2 Double values. (Which makes the .toDouble cast redundant and pointless.)

The 2nd case doesn't compile because there aren't enough hints to help the compiler.

You can fix that...

val result1 :FTDoubleDouble_Double =  _ / _

...but then you've got another problem.

scala.math.log(result1)  //error

math.log() takes a Double as the passed-in parameter, which you don't have.

Perhaps this is what you want:

val _dividedByThenLog: FTDoubleDouble_Double =
  (d1 :Double, d2 :Double) => scala.math.log(d1 / d2)

edited Sep 19, 2018 at 7:56

answered Sep 19, 2018 at 7:40

jwvh

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1 Comment

Jake Over a year ago

thanks...and yes, the toDouble is redundant. I guess I must have had an Int argument originally and forgot to delete when I changed to Double

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