val x: Int => Int = { y => y } What does this scala code mean?

Question

val x: Int=> Int = { y => y } // ① This is correct

( x1: Int) => Int = { y => y} // ② This is wrong

I understand a simple scala function like this ： x:Int => x

or this ： val f =(x: Int) => x

but how to explain the role of "x" in the sentence ①

Answer 1

In val x: Int=> Int = { y => y } , Int=> Int is used to define the return type of x immutable variable which takes Int as input and returns an Int value .

(x1: Int) => Int = { y => y} is wrong because a function cannot be assigned to another function as (x1: Int) => Int is a function and { y => y} is another function

val f =(x: Int) => x is correct as you are assigning (x: Int) => x function which takes an integer value as input and returns as it is and is assigned to a immutable variable f.

Defining x in one line would be x is a immutable input variable passed in to a function where manipulation on x is performed .

Answer 2

Here:

val x: Int=> Int = { y => y }

x is a function which receives an integer and returns the same integer.

scala> x(5)
res4: Int = 5