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In Scala programming use an anonymous function is a usual thing . when i decide to creat a vector as out put of an anonymous function from two different ways way one : var hold1=(1 to 5).map(_*2) way two: var hold2=(1 to 5).map(2*) I want to know what is the difference between those two declaration ?

Ravindu De Silva
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2 Answers2

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In short - they are exactly the same. First approach: 

var hold1 = (1 to 5).map(_*2)

Let's rewrite this another way to demonstrate what's really happening under the hood (no syntactic sugar)

var hold1 = (1 to 5).map(number => number.*(2))

Second approach:

var hold2 = (1 to 5).map(2*)

Rewrite again:

var hold2 = (1 to 5).map(number => 2.*(number))

All that is happening is in first way are invoking the * def on the number 2 and in the second way we are invoking the * def on the number.

Tanjin
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    it might be interesting to look at the generated code, however. `_ * 2` almost certainly creates an anonymous lambda, but `2 *` might not. – Rob Starling Apr 09 '17 at 02:47
  • They are only exactly the same if you assume that `Int.*` is symmetric! That is not true in the general case. – Jörg W Mittag Apr 09 '17 at 10:14
  • Why does the second version which calls the `.*` method not require the `_`? Should it not be `(1 to 5).map(2 * _)` ? – Jon Taylor Apr 09 '17 at 11:59
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Both are exactly same. You can use underscore character in many different ways. Refer this link for more details.

What are all the uses of an underscore in Scala?

Community
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Sivakumar
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