mattTea/MoneyFormatter

Example use of Higher Order Functions in Kotlin

Higher Order Functions in Kotlin - MoneyFormatter

A simple exercise to practice using higher order functions, and the patterns used in my current product team.

This can be written in one file to keep it simple.

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Overview

Work with the following function types:

typealias MoneyFormatter = (BigDecimal) -> String

typealias MoneyAdder = (BigDecimal, BigDecimal) -> String

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Steps

Step 1: Write the first functions

defaultMoneyFormatter - should take a BigDecimal and return a String (i.e. it is a MoneyFormatter)

• this will just take a BigDecimal and return it's default .toString() value

createMoneyAdder - should take a MoneyFormatter and return a MoneyAdder

• this will return a function

• the function that it returns should take two BigDecimals, add them together and format them using the MoneyFormatter that was passed in to createMoneyAdder

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Step 2: Invoke createMoneyAdder

Invoke the createMoneyAdder with the defaultMoneyFormatter to create a function that adds together and formats BigDecimals.

• use this function to add two BigDecimals together and print the output

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Step 3: Create a better MoneyFormatter

betterMoneyFormatter - should take a BigDecimal and return a String (i.e. it is a MoneyFormatter)

• this will return Truth Table A from below

Then invoke the same createMoneyAdder, but using the betterMoneyFormatter to create a function that

• adds together two BigDecimals, but formats them better
• use this function and print the output

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Step 4: (Optional) Create an even better MoneyFormatter

bestMoneyFormatter - should take a BigDecimal and return a String (i.e. it is a MoneyFormatter)

• this will return Truth Table B from below

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Truth Table A

Input	Output
0	£0.00
0.01	£0.01
1	£1.00
-1	£-1.00

Truth Table B

Input	Output
0	Free
0.01	£0.01
1	£1.00
-1	-£1.00