A closure is a function, whose return value depends on the value of one or more variables declared outside this function.
The following piece of code with anonymous function.
val multiplier = (i:Int) => i * 10
Here the only variable used in the function body, i * 10 , is i, which is defined as a parameter to the function. Try the following code −
val multiplier = (i:Int) => i * factor
There are two free variables in multiplier: i and factor. One of them, i, is a formal parameter to the function. Hence, it is bound to a new value each time multiplier is called. However, factor is not a formal parameter, then what is this? Let us add one more line of code.
var factor = 3
val multiplier = (i:Int) => i * factor
Now factor has a reference to a variable outside the function but in the enclosing scope. The function references factor and reads its current value each time. If a function has no external references, then it is trivially closed over itself. No external context is required.
Try the following example program.
Example
object Demo {
def main(args: Array[String]) {
println( "multiplier(1) value = " + multiplier(1) )
println( "multiplier(2) value = " + multiplier(2) )
}
var factor = 3
val multiplier = (i:Int) => i * factor
}
Save the above program in Demo.scala. The following commands are used to compile and execute this program.
Command
\>scalac Demo.scala
\>scala Demo
Output
multiplier(1) value = 3
multiplier(2) value = 6
