CODEWITHSUNDEEP
scala
david.perez
david.perez

Reputation: 7042

Simple function literal produces missing parameter type

With Scala 2.12, I can do this:

Try("3").fold(_.toString, _.toString)

but I can't this:

Try("3").fold(_.toString, _)

This is the error I receive:

missing parameter type for expanded function

Why a complicated expression does work and a simple one doesn't?

My workaround:

Try("3").fold(_.toString, x => x)

Upvotes: 0

Views: 57

Answers (1)

Jörg W Mittag
Jörg W Mittag

Reputation: 369614

Your first snippet is equivalent to 

Try("3").fold(x => x.toString, y => y.toString)

Your second snippet is equivalent to 

x => Try("3").fold(y => y.toString, x)

This needs a type annotation, because the type of x cannot be inferred from context.

If you want to pass the identity function, you can just pass the pre-defined identity method from Predef via η-expansion:

Try("3").fold(_.toString, identity _)

Or even implicit η-expansion:

Try("3").fold(_.toString, identity)

Upvotes: 4

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