Question

Given that there is a functionfoo[A, B, C]( func: (a: A, b: B, c: C) => B) and I want to pass in this function def secondOfThree[A, B, C](a: A, b: B, c: C): B = b

I can call foo with foo(secondOfThree) which is ugly, but works fine.. However, I would expect to be able to call foo with something along the lines of foo(case (_, b, _) => b) however this doesn’t work.

So what’s the clean idiomatic scala way of creating a simple unnamed extracting function?

Answer 1

You don’t need the case keyword, but Scala does need to know the types:

scala> def foo[A, B, C](func: (A, B, C) => B) = ...
foo: [A, B, C](func: (A, B, C) => B)Nothing

scala> foo[Symbol, Int, Char]((_, b, _) => b)

If the types are known to foo, then the call doesn’t need to specify them:

scala> def foo(func: (Symbol, Int, Char) => Int) = func('a, 2, 'c') + 5
foo: (func: (Symbol, Int, Char) => Int)Int

scala> foo((_, b, _) => b)
res3: Int = 7