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scalatypesinvocation

Obtain reference to arity-0 scala function

Scala allows functions with no parameter lists to be invoked without parentheses:

scala> def theAnswer() = 42
theAnswer: ()Int

scala> theAnswer
res5: Int = 42

How would I construct a scala expression that evaluates to the function theAnswer itself, rather than the result of theAnswer? Or in other words, how would I modify the expression theAnswer, so that the result was of type () => Int, and not type Int?

Solution

  • It can be done with:

    scala> theAnswer _
res0: () => Int = <function0>

    From the answer to the similar question:

    The rule is actually simple: you have to write the _ whenever the compiler is not explicitly expecting a Function object.

    This call will create the new instance every time, because you're "converting" method to function (what is called "ETA expansion").