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Functional Programming explained to my grandma

Anne-Honyme
7,175 views

No More NPE

Has you ever spent hours trying to find where a NPE is coming from?

This will never happen again if you use options! (🎉 they exist in Java 🎉)

To keep it simple, an option is a wrapper which accepts two kinds of content:

  • A content "value" which will be returned each time when it's possible
  • A "null" value which will be return when no correct value can be returned

In Scala, an option has no concrete type, but two implementations:

Some(object)	wrapper for a non-null value
None			wrapper for a null value

You can initialize an option to a concrete value or to null and it will return the right wrapper. An option has two opposite methods:

isEmpty		true if the option is a none
isDefined	true if the option has a value

So let's define the divide function which manages double division with the case where the divisor is equal to 0

Discover our saviour

In addition to providing us with a nice wrapper for null values, option gives us two interesting methods:

getOrElse	option.getOrElse(12)	return the value of the option if it's defined, or a default value if it's empty
fold		option.fold(0)(x => x*x)	apply the function passed in parameter if the option is defined or has a default value otherwise

Let's define the two functions:

  • Secure divide: a function which calls divide and returns the value of the option if it's possible, 0 otherwise
  • Weird divide: a function which calls divide and returns the value of the division squared, or -1
More fancy functionalities
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package example
/**
* Created by charlotte on 14/05/17.
*/
object OptionType {
val x : String = "Hello, Maybe?"
var maybe = Option(x) // Some
var maybeNot = Option(null) // None
/**
* is defined check if the option has a value
* @return true for maybe, false for maybeNot
*/
def isDefined (option :Option[String]) : Boolean ={
option.isDefined
}
/**
* is defined check if the option has no value
* @return false for maybe, true for maybeNot
*/
def isEmpty (option : Option[String]) : Boolean ={
option.isEmpty
}
val alwaysTrue = maybe.isDefined!=maybe.isEmpty
/**
* try to define a function which returns amt / divisor
* @param amt amount to divide
* @param divisor
* @return an option non if the divisor is 0, a non empty option else
*/
def divide (amt : Double, divisor: Double): Option[Double] ={
???
}
/**
* if divide is possible, return the result of divide, else return 0
*/
def secureDivide(amt: Double, divisor: Double):Double ={
???
}
/**
* if divide is possible return the square of the result, -1 else
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