Scala closure basics

closure_example1.scala

/**
  * A closure is a function, whose return value depends on the value of one or more variables
  * declared outside this function.
  */
/*
 * Example 1
 * closureIdentity has a reference to the variable i outside the function but in the enclosing scope. 
 * The function references factor and reads its current value each time. 
 */
var i = 1
val closureIdentity = () => i

closureIdentity() // 1
i = 2
closureIdentity() // 2
i = -90
closureIdentity() // -90


/*
 * Example 2
 * Identical situation but shown with a def
 */
var j = 1
def jId = j

jId // 1
j = 2
jId // 2
j = -90
jId // -90


/*
 * Example 3 - initialising the closed-over variable inside the value declaration
 */
val closureIncrement: () => Int = { var offset = 0; () => { offset += 1; offset }}

closureIncrement() // 1
closureIncrement() // 2
closureIncrement() // 3