Published October 31, 2019
Updated February 16, 2020

# Ruby Truth Tables

Demonstrates how to build and use truth tables.

## Transcript

`# Hello and welcome to the Alchemists Screencasts! # Today, we'll look at using Truth Tables in Ruby. # Let's say we have three boolean values and want to know all possible lookup combinations:`

`# value 1 | value 2 | value 3 | combination index # ----------+---------+----------+------------------- # 1 | 1 | 1 | 0 # 1 | 1 | 0 | 1 # 1 | 0 | 1 | 2 # 1 | 0 | 0 | 3 # 0 | 1 | 1 | 4 # 0 | 1 | 0 | 5 # 0 | 0 | 1 | 6 # 0 | 0 | 0 | 7`

`irb`

`table = [true, false].repeated_permutation(3).to_a # If it helps, here is what this looks like via Awesome Print: ap table # With our truth table in hand, we can ask the table for the index of any combination: table.index [true, true, true] table.index [true, false, true] table.index [false, false, false] # Moving this logic to a method, we can provide some syntatic sugar. def truth_table_index(*combinations) [true, false].repeated_permutation(3) .to_a .then { |table| table.index combinations } end # There is no longer a need to build new arrays like before. # We can pass in the boolean combination values instead. truth_table_index true, true, true truth_table_index true, false, true truth_table_index false, false, false exit`

`# Note that bit shifting would be more performant. # Yet, it is good to know we can use arrays for representing truth tables. # Enjoy! # https://alchemists.io # ☿ 🜔 🜍 🜂 🜃 🜁 🜄`