Scala：如何使闭包不更改其自由变量？

Question

In the following code snippet, closure foo see the changes made in x as it should in scala. However, how can I make local variable y in foo hold value of x permanently and not see changes?

scala> var x = 10
x: Int = 10

scala> val foo = (a:Int) => {val y = x; a + y}
foo: Int => Int = <function1>

scala> foo(3)
res1: Int = 13

scala> x = 5
x: Int = 5

scala> foo(3)    //see changes made in x. But how can I make closure not to see changes made on x?
res2: Int = 8

Answer 1

You could do something like this:

val foo = ((x:Int) => (a:Int) => {val y = x; a + y})(x)

In this case, x is bound in foo.

What you are doing is an example of closure .

Answer 2

scala> var x = 10 x: Int = 10 scala> val foo = { val y = x; (a: Int) => a + y } foo: Int => Int = $$Lambda$1027/1344946518@5416f8db scala> foo(3) res0: Int = 13 scala> x = 5 x: Int = 5 scala> foo(3) res1: Int = 13