\documentclass[10pt,a4paper]{article}

% Packages
\usepackage{fancyhdr}           % For header and footer
\usepackage{multicol}           % Allows multicols in tables
\usepackage{tabularx}           % Intelligent column widths
\usepackage{tabulary}           % Used in header and footer
\usepackage{hhline}             % Border under tables
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\usepackage{xcolor}             % For hex colours
%\usepackage[utf8x]{inputenc}    % For unicode character support
\usepackage[T1]{fontenc}        % Without this we get weird character replacements
\usepackage{colortbl}           % For coloured tables
\usepackage{setspace}           % For line height
\usepackage{lastpage}           % Needed for total page number
\usepackage{seqsplit}           % Splits long words.
%\usepackage{opensans}          % Can't make this work so far. Shame. Would be lovely.
\usepackage[normalem]{ulem}     % For underlining links
% Most of the following are not required for the majority
% of cheat sheets but are needed for some symbol support.
\usepackage{amsmath}            % Symbols
\usepackage{MnSymbol}           % Symbols
\usepackage{wasysym}            % Symbols
%\usepackage[english,german,french,spanish,italian]{babel}              % Languages

% Document Info
\author{pixelus}
\pdfinfo{
  /Title (ruby-essentials.pdf)
  /Creator (Cheatography)
  /Author (pixelus)
  /Subject (Ruby Essentials Cheat Sheet)
}

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% This two commands together give roughly
% the right line height in the tables
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% Commands
\newcommand{\SetRowColor}[1]{\noalign{\gdef\RowColorName{#1}}\rowcolor{\RowColorName}} % Shortcut for row colour
\newcommand{\mymulticolumn}[3]{\multicolumn{#1}{>{\columncolor{\RowColorName}}#2}{#3}} % For coloured multi-cols
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% Font and Colours
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\color{TextColor}

% Header and Footer
\pagestyle{fancy}
\fancyhead{} % Set header to blank
\fancyfoot{} % Set footer to blank
\fancyhead[L]{
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{C}
    \SetRowColor{DarkBackground}
    \vspace{-7pt}
    {\parbox{\dimexpr\textwidth-2\fboxsep\relax}{\noindent
        \hspace*{-6pt}\includegraphics[width=5.8cm]{/web/www.cheatography.com/public/images/cheatography_logo.pdf}}
    }
\end{tabulary}
\columnbreak
\begin{tabulary}{11cm}{L}
    \vspace{-2pt}\large{\bf{\textcolor{DarkBackground}{\textrm{Ruby Essentials Cheat Sheet}}}} \\
    \normalsize{by \textcolor{DarkBackground}{pixelus} via \textcolor{DarkBackground}{\uline{cheatography.com/125267/cs/24072/}}}
\end{tabulary}
\end{multicols}}

\fancyfoot[L]{ \footnotesize
\noindent
\begin{multicols}{3}
\begin{tabulary}{5.8cm}{LL}
  \SetRowColor{FootBackground}
  \mymulticolumn{2}{p{5.377cm}}{\bf\textcolor{white}{Cheatographer}}  \\
  \vspace{-2pt}pixelus \\
  \uline{cheatography.com/pixelus} \\
  \end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Cheat Sheet}}  \\
   \vspace{-2pt}Not Yet Published.\\
   Updated 25th August, 2020.\\
   Page {\thepage} of \pageref{LastPage}.
\end{tabulary}
\vfill
\columnbreak
\begin{tabulary}{5.8cm}{L}
  \SetRowColor{FootBackground}
  \mymulticolumn{1}{p{5.377cm}}{\bf\textcolor{white}{Sponsor}}  \\
  \SetRowColor{white}
  \vspace{-5pt}
  %\includegraphics[width=48px,height=48px]{dave.jpeg}
  Measure your website readability!\\
  www.readability-score.com
\end{tabulary}
\end{multicols}}




\begin{document}
\raggedright
\raggedcolumns

% Set font size to small. Switch to any value
% from this page to resize cheat sheet text:
% www.emerson.emory.edu/services/latex/latex_169.html
\footnotesize % Small font.

\begin{multicols*}{2}

\begin{tabularx}{8.4cm}{X}
\SetRowColor{DarkBackground}
\mymulticolumn{1}{x{8.4cm}}{\bf\textcolor{white}{Generalities}}  \tn
% Row 0
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{8.4cm}}{\{\{nobreak\}\}Everything in Ruby is an object.} \tn 
% Row Count 1 (+ 1)
% Row 1
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{nobreak\}\}A method always return exactly one single thing (an object).} \tn 
% Row Count 3 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\mymulticolumn{1}{x{8.4cm}}{\{\{nobreak\}\}We can use do and end inplace of \{ \}.} \tn 
% Row Count 4 (+ 1)
% Row 3
\SetRowColor{white}
\mymulticolumn{1}{x{8.4cm}}{\{\{nobreak\}\}Create a comment with \#.} \tn 
% Row Count 5 (+ 1)
\hhline{>{\arrayrulecolor{DarkBackground}}-}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.04 cm} x{4.96 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Printing Data}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}print "string" & print data to the screen without adding a new line at the end \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}puts "string" & print data to the screen and add an automatic new line \tn 
% Row Count 6 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}p "string" & print data to the screen with a new line and give information on type of data \tn 
% Row Count 10 (+ 4)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.6 cm} x{4.4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Special Characters}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}\textbackslash{}n & add a new line \tn 
% Row Count 1 (+ 1)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}\textbackslash{}t & add a tabulation \tn 
% Row Count 2 (+ 1)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.84 cm} x{4.16 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Conversions}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}string.split(" ") & convert a string into an array \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}array.join(" ") & convert an array into a string \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}string.to\_i & convert a string to an integer \tn 
% Row Count 6 (+ 2)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}element.to\_s & convert an element to a string \tn 
% Row Count 8 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}element.to\_a & convert an element to an array \tn 
% Row Count 10 (+ 2)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}num.to\_f & convert an integer to a float \tn 
% Row Count 12 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Ranges}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}(start..end).each \{ |ele| … \} & specify a range of numbers including end \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}(start...end).each \{ |ele| … \} & specify a range of numbers excluding end \tn 
% Row Count 6 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Iterators}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}number.times \{…\} & repeat a block a number of times \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}array.each \{ |ele| ... \} & iterate over element of an array \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.each\_with\_index \{ |ele, i| ... \} & iterate over elements of an array with index \tn 
% Row Count 7 (+ 3)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}string.each\_char \{ |char| ... \} & iterate over characters of a string \tn 
% Row Count 10 (+ 3)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}string.each\_char.with\_index \{ |char, i| ... \} & iterate over characters of a string with index \tn 
% Row Count 14 (+ 4)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}hash.each \{ |key, val| ... \} & iterate over elements of a hash \tn 
% Row Count 16 (+ 2)
% Row 6
\SetRowColor{LightBackground}
\{\{nobreak\}\}hash.each\_key \{ |key| ... \} & iterate over keys of a hash \tn 
% Row Count 18 (+ 2)
% Row 7
\SetRowColor{white}
\{\{nobreak\}\}hash.each\_value \{ |val| ... \} & iterate over values of a hash \tn 
% Row Count 21 (+ 3)
% Row 8
\SetRowColor{LightBackground}
\{\{nobreak\}\}element.inject \{ |acc, el| acc + el \} & return the value for the method where each element of the block is passed in an accumulator value and the current element \tn 
% Row Count 28 (+ 7)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.2 cm} x{4.8 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Arrays}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.push & add element(s) to the end of an array \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}array.unshift & add element(s) to the front of an array \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.pop & remove the last element of an array \tn 
% Row Count 6 (+ 2)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}array.shift & remove the first element of an array \tn 
% Row Count 8 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.include?() & check if an element exists in an array \tn 
% Row Count 10 (+ 2)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}array.index & find the index of an element in an array \tn 
% Row Count 12 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Objects}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}element.is\_a? (Object) & return true if class is the class of Object, or if class is one of the superclasses of Object or modules included in Object \tn 
% Row Count 7 (+ 7)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}element.object\_id & return the memory address of some data \tn 
% Row Count 9 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}prc = Proc.new \{ |ele| ele * 2 \} & proc, an object that contains a block and allow to save blocks to variables \tn 
% Row Count 13 (+ 4)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}p prc.call(5) & call the proc and evaluate to the last line of code executed within the block \tn 
% Row Count 17 (+ 4)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}\&prc & convert a block into a proc or convert a proc into a block, \& in the parameters for a method definition will convert a block to a proc, \& in the arguments for a method call  will convert a proc to a block \tn 
% Row Count 28 (+ 11)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}obj.instance\_of? Class & return true if obj is an instance of the given class \tn 
% Row Count 31 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{8.4cm}}{{\bf{If we don't intend to mutate a string, we can use a symbol to save some memory because a symbol value will be stored in exactly one memory location. So they are often used to act as unique identifiers.}}}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.76 cm} x{4.24 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Enumerables}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.all? \{ |ele| … \} & return true when all elements result in true \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}array.any? \{ |ele| … \} & return true when at least one element result in true \tn 
% Row Count 6 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.none? \{ |ele| … \} & return true when no element result in true \tn 
% Row Count 8 (+ 2)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}array.one? \{ |ele| … \} & return true when exactly one element result in true \tn 
% Row Count 11 (+ 3)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.map \{ |ele| ... \} & return a new array containing the values returned by the block \tn 
% Row Count 14 (+ 3)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}array.sum & return the total sum of all elements \tn 
% Row Count 16 (+ 2)
% Row 6
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.min & return the minimum element \tn 
% Row Count 18 (+ 2)
% Row 7
\SetRowColor{white}
\{\{nobreak\}\}array.max & return the maximum element \tn 
% Row Count 20 (+ 2)
% Row 8
\SetRowColor{LightBackground}
\{\{nobreak\}\}array.flatten & return the 1 dimensional version of any multidimensional array \tn 
% Row Count 23 (+ 3)
% Row 9
\SetRowColor{white}
\{\{nobreak\}\}array.select & return an array containing all elements of enum for which the given block returns a true value \tn 
% Row Count 28 (+ 5)
% Row 10
\SetRowColor{LightBackground}
\{\{nobreak\}\}element.length & return a number representing the length of the element \tn 
% Row Count 31 (+ 3)
\end{tabularx}
\par\addvspace{1.3em}

\vfill
\columnbreak
\begin{tabularx}{8.4cm}{x{3.76 cm} x{4.24 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Enumerables (cont)}}  \tn
% Row 11
\SetRowColor{LightBackground}
\{\{nobreak\}\}element.count & return a number representing the count of elements that result in true \tn 
% Row Count 4 (+ 4)
% Row 12
\SetRowColor{white}
\{\{nobreak\}\}element.last & return the last element of a string or an array \tn 
% Row Count 7 (+ 3)
% Row 13
\SetRowColor{LightBackground}
\{\{nobreak\}\}element.last(num) & return a substring from the end of the string until it reaches the num value (counting backwards), or return a copy if the given limit is greater than or equal to the string length \tn 
% Row Count 16 (+ 9)
% Row 14
\SetRowColor{white}
\{\{nobreak\}\}num.even? & return true if the number is even \tn 
% Row Count 18 (+ 2)
% Row 15
\SetRowColor{LightBackground}
\{\{nobreak\}\}num.odd? & return true if the number is odd \tn 
% Row Count 20 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.52 cm} x{4.48 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Inpout / Output}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}require File & import File when gems are involved \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}require\_relative File & import File with a path to another ruby file \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}element = gets & allow a user to give input and add a newline character at the end \tn 
% Row Count 7 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.6 cm} x{4.4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Scope}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}\$message = "something" & create a global variable, everywhere area in the code can access the global scope \tn 
% Row Count 4 (+ 4)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}\$PROGRAM\_NAME & global variable, string describing the name of the program \tn 
% Row Count 7 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}\$stdin & global variable that holds a stream for the standard input \tn 
% Row Count 10 (+ 3)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}\$stdout & global variable which holds the standard output stream \tn 
% Row Count 13 (+ 3)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}CONSTANT & constant variable, cannot be reassigned and begin the name with a capital letter \tn 
% Row Count 17 (+ 4)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.92 cm} x{4.08 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Strings}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}string.downcase & return a copy of str with all downcase letters \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}string.upcase & return a copy of str with all uppercase letters \tn 
% Row Count 6 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}string.c​ap​italize & return a copy of str with the first character converted to uppercase \tn 
% Row Count 10 (+ 4)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}string.reverse & return a new string with the characters in reverse order \tn 
% Row Count 13 (+ 3)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}string.chomp & remove the last character if it's a newline or carriage return \tn 
% Row Count 17 (+ 4)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}string.index​(po​sition) & return the character in the specified position \tn 
% Row Count 20 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Hashes}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}hash = Hash.new OR hash = \{\} & create a new hash \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}hash = Hash.new(...) & create a new hash with a default value \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}Hash.new \{ |h, k| h{[}k{]} = {[}{]} \} & create a new hash and define default value as an array \tn 
% Row Count 7 (+ 3)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}hash{[}key{]} & return value of the hash key \tn 
% Row Count 9 (+ 2)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}hash.has\_key?() & check if a key exists in a hash \tn 
% Row Count 11 (+ 2)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}hash.has\_value?() & check if a value exists in a hash \tn 
% Row Count 13 (+ 2)
% Row 6
\SetRowColor{LightBackground}
\{\{nobreak\}\}hash.sort\_by \{|k, v| v\} & return the value in ascending order in a new array \tn 
% Row Count 16 (+ 3)
% Row 7
\SetRowColor{white}
\{\{nobreak\}\}hash.sort\_by \{|k, v| -v\} & return the value in descending order in a new array \tn 
% Row Count 19 (+ 3)
% Row 8
\SetRowColor{LightBackground}
\{\{nobreak\}\}hash.sort\_by \{|k, v| {[}-v, k{]}\} & sort the hash by the values in descending order and sort it by letter's alphabetical order in a new array \tn 
% Row Count 25 (+ 6)
% Row 9
\SetRowColor{white}
\{\{nobreak\}\}\{ |a, b| a.to\_s \textless{}=\textgreater{} b.to\_s \} & sort the numbers alphabetically by characters \tn 
% Row Count 28 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Symbols}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}\&:symbol & turn the symbol into a simple proc, equivalent to: element.method \{ |ele| ele.symbol\_method \} \tn 
% Row Count 5 (+ 5)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}hash = \{:k1 =\textgreater{} "v1", :k2=\textgreater{} "v2"\} & initializing a hash with symbol keys allows to drop the rocket (=\textgreater{}) and move the colon (:) to the right of the symbol \tn 
% Row Count 11 (+ 6)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{8.4cm}}{{\bf{Symbols are immutable and can never been changed.}} \newline {\bf{If we don't intend to mutate a string, we can use a symbol to save some memory because a symbol value will be stored in exactly one memory location. So they are often used to act as unique identifiers.}}}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Operators}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}def method(arg\_1, arg\_2,  *other\_args) & accept additional arguments and stock them into an array \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}method(*array) & pass  an array into a function expecting multiple arguments \tn 
% Row Count 6 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}method(**hash) & pass a hash into a function expecting multiple arguments \tn 
% Row Count 9 (+ 3)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}array = {[}*arr\_1, element, *arr\_2{]} & decompose an array into individual items where each individual element become an argument \tn 
% Row Count 14 (+ 5)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}hash = {[}*some\_hash, symbol: value{]} & decompose a hash into individual items where each individual element become an argument, only work with hashes where the keys are symbols \tn 
% Row Count 21 (+ 7)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}element\_1 \textless{}=\textgreater{} element\_2 & compare two values and return -1, 0, or 1 \tn 
% Row Count 24 (+ 3)
% Row 6
\SetRowColor{LightBackground}
\{\{nobreak\}\}a ||= b & assign b to a iff a is nil or false \tn 
% Row Count 26 (+ 2)
% Row 7
\SetRowColor{white}
\{\{nobreak\}\}a \&\&= b & assign b to a if a is true or not nil \tn 
% Row Count 28 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.12 cm} x{4.88 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Class}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}initialize & put define default argument \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}@variable & d inside \#initializeinstance variable or attribute of class, typically assigned inside \#initialize, changing the variable will only effect that one instance \tn 
% Row Count 9 (+ 7)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}@@variable & class variable, typically assigned inside of the class, but not inside of \#initialize, changing the variable will effect all instances because all instances of the class \tn 
% Row Count 17 (+ 8)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}CLASS\_CONSTANT & class constant, will be shared among all instances of a class, but cannot be changed \tn 
% Row Count 21 (+ 4)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}attr\_r​eader & instance variable getter \tn 
% Row Count 23 (+ 2)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}attr\_writer & instance variable setter \tn 
% Row Count 25 (+ 2)
% Row 6
\SetRowColor{LightBackground}
\{\{nobreak\}\}attr\_a​ccesor & instance variable getter and setter \tn 
% Row Count 27 (+ 2)
% Row 7
\SetRowColor{white}
\{\{nobreak\}\}Class.new & create a new anonymous (unnamed) class \tn 
% Row Count 29 (+ 2)
% Row 8
\SetRowColor{LightBackground}
\{\{nobreak\}\}def method & instance method we can only call it on a Class instance we initialized using Class.new, instance method depends on the attributes or instance variables of an instance \tn 
% Row Count 36 (+ 7)
\end{tabularx}
\par\addvspace{1.3em}

\vfill
\columnbreak
\begin{tabularx}{8.4cm}{x{3.12 cm} x{4.88 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Class (cont)}}  \tn
% Row 9
\SetRowColor{LightBackground}
\{\{nobreak\}\}def self.method & class method called directly on the class, self refers to the Class itself and cannot refer to any instance attributes like @variable (Class::method) \tn 
% Row Count 7 (+ 7)
% Row 10
\SetRowColor{white}
\{\{nobreak\}\}Queue.new & create a queue, process work in FIFO (first-in-first-out) order \tn 
% Row Count 10 (+ 3)
% Row 11
\SetRowColor{LightBackground}
\{\{nobreak\}\}Class::CONSTANT & access to the constant inside the class \tn 
% Row Count 12 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{8.4cm}}{{\bf{To create a class we use the class keyword.}} \newline {\bf{The name of a class must begin with a capital letter.}} \newline {\bf{We can define methods within a class.}}}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.92 cm} x{4.08 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Syntactic Sugar}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}el\_1.==(el\_2) & equivalent to: el\_1 == el\_2 \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}element.{[}{]}(num) & equivalent to: element{[}num{]} \tn 
% Row Count 4 (+ 2)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}el.{[}{]}=(num, string) & equivalent to: el{[}num{]} = string \tn 
% Row Count 6 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Debugging with Byebug}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}require "byebug" & add to the top of your file to gain access to the gem \tn 
% Row Count 3 (+ 3)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}debugger & place this line at a point in your file where you want to begin debugger mode \tn 
% Row Count 7 (+ 4)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}l \textless{}start line\textgreater{}-\textless{}end line\textgreater{} & list the line numbers in the specified range \tn 
% Row Count 10 (+ 3)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}step OR s & step into the method call on the current line,  once execution is paused on a line containing a method call \tn 
% Row Count 16 (+ 6)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}next OR n & move to the next line of executed code \tn 
% Row Count 18 (+ 2)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}break \textless{}line num\textgreater{} OR b \textless{}line num\textgreater{} & place a breakpoint at the specified line number, this will pause execution \tn 
% Row Count 22 (+ 4)
% Row 6
\SetRowColor{LightBackground}
\{\{nobreak\}\}continue OR c & resume normal execution of the code until a breakpoint \tn 
% Row Count 25 (+ 3)
% Row 7
\SetRowColor{white}
\{\{nobreak\}\}display \textless{}variable\textgreater{} & automatically show the current value of a variable \tn 
% Row Count 28 (+ 3)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{4 cm} x{4 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Testing with Rspec}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}describe & name the method being tested \tn 
% Row Count 2 (+ 2)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}it & expresse the expected behavior of the method being tested \tn 
% Row Count 5 (+ 3)
% Row 2
\SetRowColor{LightBackground}
\{\{nobreak\}\}expect & show how that behavior is tested \tn 
% Row Count 7 (+ 2)
% Row 3
\SetRowColor{white}
\{\{nobreak\}\}context & additional blocks to outline different scenarios that code is expected to satisfy \tn 
% Row Count 12 (+ 5)
% Row 4
\SetRowColor{LightBackground}
\{\{nobreak\}\}Class\#method & refers to the instance method in the class \tn 
% Row Count 15 (+ 3)
% Row 5
\SetRowColor{white}
\{\{nobreak\}\}Class.method OR Class::method & refers to the class method in the class \tn 
% Row Count 17 (+ 2)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\SetRowColor{LightBackground}
\mymulticolumn{2}{x{8.4cm}}{{\bf{To use RSpec, we need to separate our implementation code files from the testing files using a /lib and /spec folder respectively.}} \newline  \newline /example\_project \newline   ├── lib \newline   │   ├── add.rb \newline   │   └── prime.rb \newline   └── spec \newline       ├── add\_spec.rb \newline       └── prime\_spec.rb}  \tn 
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}

\begin{tabularx}{8.4cm}{x{3.52 cm} x{4.48 cm} }
\SetRowColor{DarkBackground}
\mymulticolumn{2}{x{8.4cm}}{\bf\textcolor{white}{Exceptions}}  \tn
% Row 0
\SetRowColor{LightBackground}
\{\{nobreak\}\}begin...rescue...end & react to an exception, the code in the begin block will execute until an exception is reached, once an exception is reached, the execution will immediately jump to rescue \tn 
% Row Count 8 (+ 8)
% Row 1
\SetRowColor{white}
\{\{nobreak\}\}raise & bring up an exception,  flag an exceptional scenario that should be handled in a specific way \tn 
% Row Count 13 (+ 5)
\hhline{>{\arrayrulecolor{DarkBackground}}--}
\end{tabularx}
\par\addvspace{1.3em}


% That's all folks
\end{multicols*}

\end{document}