Scala IDE warning: "anonymous function convertible to method value"
First, If you want to create an "alias" for method, that's enough:
scala> val foo = bar(_) //val instead of def, still warning from Idea
foo: Int => Int = <function1>
Second, this shoud remove Idea's warning:
scala> val foo = bar _
foo: Int => Int
Actually, it's not just alias - your method becomes converted into a function (eta-expansion). You cant' just specify method (compile-time entity) as compiler will expect parameters - you need to convert it into a function (using underscore) first. Sometimes it's done automatically when compiler expects a function:
scala> val foo: Int => Int = bar
foo: Int => Int = <function1>
So this probably what Idea wants from you. In other cases - you have to use eta-expansion operator (_
) explicitly.
P.S/1. def foo = bar(_)
(def
instead of val
) makes no sense as it will return new (but same) function every time, val
(or lazy val
to be safe from NullPointerException
) just returns it once.
P.S/2. The difference between (_)
and _
is that first is partially applied function (which does _
eta-expansion automatically), which means that for let's say:
scala> def bar(a: Int, b: Int) = a
bar: (a: Int, b: Int)Int
scala> def foo = bar _
foo: (Int, Int) => Int
scala> def foo = bar(_)
<console>:8: error: missing parameter type for expanded function ((x$1) => bar(x$1))
def foo = bar(_)
^
<console>:8: error: not enough arguments for method bar: (a: Int, b: Int)Int.
Unspecified value parameter b.
def foo = bar(_)
^
scala> def foo = bar(_, _)
foo: (Int, Int) => Int
you have to specify bar(_, _)
as there are two arguments.
That's a suggestion from IntelliJ. If you click "More" in the suggestion, you'll see the following (sorry it's graphic, I can't copy the text):
You can either ignore or use bar _
instead of bar(_)
.