resource11 / ruby-vs-js

Programming Fundamentals in Ruby (versus JavaScript)

You've alredy learned the basics of programming with JavaScript, and you've begun to think like a problem-solver. You've had practice reading JS code and predicting execution by evaluating expressions in your mind.

We'll continue to reinforce the basics of programming, but this time with Ruby. This may seem like a lot of material to cover in a short time, but the truth is our task is simpler than it was when we introduced JS. Instead of teaching you how to program, we'll focus on the differences between Ruby and JS with the goal of utilizing the foundation we've already built.

"Polyglot" is a term used to refer to someone who can use two or more programming languages. By learning two languages, we increase your understanding of basic programming concepts, as well as give you an edge in job market.

You will reference this material again and again over the next few weeks. Focus on noting the differences between Ruby and JS. You should use this material as you would the HyperPolyglot reference: not as reading material, but as a handy place to compare and contrast the two most popular languages for web development.

Prerequisites

• ga-wdi-boston/js-basics
• ga-wdi-boston/js-reference-types

Objectives

By the end of this, students should be able to:

• Contrast Ruby REPL and interpreter with Node interpreter/REPL.
• Contrast basic language features and types from Ruby with basic language features and types from JavaScript.
• Rewrite a JavaScript script in Ruby.

Preparation

1. Fork and clone this repository.
2. Install dependencies with bundle install.

Outline

In order to accomplish our learning objectives, we've got quite a number of comparisons to make between Ruby and Javascript. These include:

• Running scripts from the command line.
• Evaluating code interactively in a REPL.
• Variable declaration and naming conventions.
• Strings, interpolation, and concatenation.
• Methods and functions, including predicates.
• Fixnums, Floats, and Numbers.
• Falsiness.
• Flow control.
• Loops, ranges, and enumerable iteration.
• Implicit and explicit returns.
• Expression evaluation and conditional assignment.
• Type coercion.
• Logic, shortcut evaluation, and operator precedence.

Foreword

The depth and breadth of the Ruby Core and Standard Library are so extensive that we'll always want to check them before building something ourselves. The official Ruby docs are our friends, and we should use them liberally. Over time, we'll learn to remember the more common methods, but even then it can be extremely useful to consult the documentation.

Pry

gem install pry
pry

Pry is a console-based REPL for working with Ruby. Simply type in an expression into Pry, and it returns the result (preceded by => , also known as a 'hash rocket').

[1] pry(main)> 1 + 1
=> 2
[2] pry(main)>

In addition to allowing us to run code one line at a time, Pry can also be used (like the node-debug REPL we saw in Unit 1) to interactively debug our code. Though we won't be focusing on that aspect of Pry today, it'll be a critical tool throughout the rest of this unit.

Let's use pry to explore some of the core differences between Ruby and JavaScript.

Ruby vs JS :: Core Syntax, Variables, and Operators

Semicolons

One of the first things you might notice about Ruby is a conspicuous lack of semicolons.

[1] pry(main)> 1
=> 1

The end of a line (almost always) marks the end of an expression; semicolons are only required if you have two distinct expressions on one line (e.g. name = "Antony"; age = 35). The most likely place where you might spot a semicolon in Ruby is inside a for loop, and those (as you'll soon see) are used very infrequently in Ruby.

Variable Declaration

Another huge difference between Ruby and JavaScript is how variables are handled. In JavaScript, a variable must be declared (using var) before it can be used or accessed. In Ruby, this is not the case. Variables in Ruby can simply be defined, without having previously been declared.

[1] pry(main)> a = 1
=> 1

However, this only works if we assign the variable a value. Why? Because otherwise, Ruby will default to trying to evaluate your variable, and because you haven't defined it yet, Ruby will throw an error.

[1] pry(main)> counter
NameError: undefined local variable or method 'counter' for main:Object
from (pry):1:in '__pry__'
[2] pry(main)> counter = 0
=> 0
[3] pry(main)> counter
=> 0
[4] pry(main)>

Ruby has its own set of scoping rules for variables, just like JavaScript does, and they work in (mostly) similar ways.

Operators

In Ruby, everything is an expression - a statement composed of a combination of operands (data) and operations. In JavaScript, things like + and - are true operators - keywords built into the language itself, and embued with fixed, unchangeable meanings. In Ruby, in contrast, most "operators" you encounter are actually method calls on some object; the main exceptions are assignment operators (e.g. =), logical operators (e.g. ||, &&, !), and control flow operators (e.g. and, or, not).

Brief Aside: Syntactic Sugar

Ruby doesn't have an increment operator, either pre (++i) or post (i++). Use += instead.

[4] pry(main)> counter += 1
=> 1
[5] pry(main)> counter += 1
=> 2
[6] pry(main)> counter
=> 2
[7] pry(main)>

counter += 1 is really just Ruby making you type fewer characters to accomplish counter = counter + 1. This is commonly referred to as 'syntactic sugar' - when a programming language has syntax that's deliberately designed to make code shorter/more semantic/easier to write. Ruby has a ton of syntactic sugar. JavaScript allows us to use this shorthand too; however, Ruby takes things a step further, providing this 'syntactic sugar' for a variety of operators, including *, -, and even ||.

[1] pry(main)> counter ||= 0          # counter = counter || 0
=> 0
[2] pry(main)> counter += 1           # counter = counter + 1
=> 1
[3] pry(main)> counter *= 5           # counter = counter * 5
=> 5
[4] pry(main)> counter -= 1           # counter = counter - 1
=> 4

Your Turn

In pairs, open up pry and take five minutes trying out the operators we've used in JavaScript on numbers and numeric variables. Does anything surprising or confusing happen? Write those things down to share with the class. Have a look in operator_examples.rb if you need some prompts.

Ruby vs JS :: Strings

Strings in Ruby are pretty similar to strings in JavaScript. To see all the methods that strings have in Ruby, open up pry, type a string followed by a '.', and hit tab; alternatively, you can call "some string".methods.sort for a full list. And, of course, the Ruby documentation has a full list as well.

Strings objects come with several conversion methods that all start to_ and then a letter or abbreviation hinting at what conversion they perform. to_i and to_f are used commonly - these convert the string into one of two types of numbers, integers (whole numbers) and floats (decimal numbers).

String interpolation

Ruby, unlike JavaScript, attributes different meanings to single-quoted and double-quoted strings. Single-quoted strings are referred to as 'string literals'; they interpret their contents as a literal sequence of characters, with only two recognized escape sequences - \' and \\. Double-quoted strings, in contrast, support a much wider variety of escape characters, including \n (new line), \t (tab), and \s (space); if \n appeared in a single-quoted string, it would be interpreted as the character \ followed by the character \n, rather than a new line.

One neat thing that comes out of this is the ability to do string interpolation, inserting variables directly into the middle of a string. In JavaScript, if we had a variable name with value '"Harry"' and wanted to print out "Hello, Harry!", we would need to write

console.log("Hello, " + name + "!");

  "Hello, Harry!"

That's not too bad, but if you start doing this with multiple variables, it can get a little hairy.

names = ["Harry", "Ron", "Hermione"]
console.log("Hello, " + names[0] + ", " + names[1] + ", and " + names[2] + "!");

  "Hello, Harry, Ron, and Hermione!"

Keeping track of all of those quotes is a pain (not to mention the spaces), and if you forget a +, the expression won't work. And it gets even worse in Ruby, because Ruby doesn't implicitly convert numbers to strings, so all those conversions need to be done manually using .to_s.

[1] pry(main)> name = "Matt"
=> "Matt"
[2] pry(main)> age = 28
=> 28
[3] pry(main)> puts age
28
=> nil
[4] pry(main)> puts name + " is " + age + " years old"
TypeError: no implicit conversion of Fixnum into String
from (pry):3:in '+'
[5] pry(main)> puts name + " is " + age.to_s + " years old"
=> "Matt is 28 years old"

Fortunately, Ruby does give us an alternative - at least with double-quoted strings. If the sequence #{ ... } appears inside a double-quoted string, Ruby will replace it with the value of the expression inside the curly braces, converted to a string.

So instead of:

[1] pry(main)> name = "Matt"
=> "Matt"
[2] pry(main)> age = 28
=> 35
[3] pry(main)> name + " is " + age.to_s + " years old."
=> "Matt is 28 years old."

We can use:

[1] pry(main)> name = "Matt"
=> "Matt"
[2] pry(main)> age = 28
=> 28
[4] pry(main)> "#{name} is #{age} years old"
=> "Matt is 28 years old"

This also works:

[5] pry(main)> "ten + seven == #{10 + 7}"
=> "ten + seven == 17"

Your Turn

In your pairs, go to the Ruby documentation for strings (link above), and look up three of the methods available to Ruby strings. Open up pry and test them out on some sample strings. Try to incorporate string interpolation at least once. Once you're done, we'll reconvene as a class and discuss the methods we've explored.

Ruby vs JS :: Flow Control

Conditionals

// JavaScript version
if (name === "Max") {
  console.log("It's Max");
} else if (name === "Matt") {
  console.log("It's Matt");
} else {
  console.log("Not Max or Matt");
}

# Ruby version
if name == "Max"
  puts "It's Max"
elsif name == "Matt"
  puts "It's Matt"
else
  puts "Not Max or Matt"
end

A Ruby if looks quite similar to a JavaScript if. Some of the major differences are:

• In Ruby, we use elsif, not else if.
• Conditions don't require parentheses (though they can still accept them).
• No curly braces required. Simply break up your condition from your code with a newline (as above), a semicolon, or the keyword then (e.g. if .... then ).
• The end of the if is indicated by the keyword end. end is an extremely common keyword in Ruby, appearing at the end of pretty much any contiguous section of code.

unless can sometimes be used to replace an if with a negated test and no elsif or else.

if !(name == "Max")
  puts "Not Max!"
end

becomes

unless name == "Max"
  puts "Not Max!"
end

Loops

Similarly to if, a while loop also looks almost the same in Ruby as it does in JavaScript.

while i < 10 do
  i += 1
end

The do keyword above is optional - a newline is sufficient - but do ... end is a common construction in Ruby because it specifies what's known as a block, a grouping of several lines of code. We'll learn more about blocks soon.

Your Turn

This time, rather than using pry, we're going to write a longer program in Sublime, and then run it in the terminal using ruby, a command line Ruby environment. Open up the file fizzbuzz.rb, found in the root of this repo; in pairs, you're going to solve "FizzBuzz", a simple programming challenge based on a childrens' game. Essentially, your program should print out all of the numbers from 1 up to max_num, which is a variable to which you can assign an arbitrary (positive, integer) value. However, if a number is divisible by 3, instead of printing the number, your program should print the word "fizz"; for numbers divisible by 5, it should print "buzz"; for numbers divisible by both 3 and five, it should print "fizzbuzz".

To run your code, simply type navigate to the root of this repository and run ruby fizzbuzz.rb

This should seem familiar, since it's exactly what we were doing with node in Unit 1. It's a deliberate similarity - Node was modeled off of other console-based runtime environments, as a way of giving JavaScript a solid platform for running on the server side.

Ruby vs JS :: Methods

Ruby draws no distinction between functions that are properties of objects and functions that aren't; in Ruby, all of them are called 'methods'.

To define a method, you use the following syntax:

def square? (num)
  Math.sqrt(num).to_i**2 == num
end

The question mark is conventional for methods that return a boolean. Another common convention in Ruby is a trailing exclamation point, which indicates that a method is a 'mutator' - this means that the method changes the object that it is called from, rather than returning a new object.

This behavior is also sometimes referred to as operating 'in place'.

Ruby methods use an implicit return - by default, they will return the value last expression evaluated (which may or may not be a return expression). However, Ruby does also have a return keyword which, as it does in JavaScript, immediately terminates the function/method and sends back a value. In the case of the method above, square? will return the value of that last expression, Math.sqrt(num).to_i**2 == num.

Your Turn

Take your code from the previous exercise and turn it into a method called fizzbuzz; this method should accept an argument, max_num.

At the end of your program, add the following two lines:

binding.pry
""

binding.pry inserts a breakpoint into the program; this will cause the program to stop and let us look around. The second line, with the empty string, is only necessary because binding.pry won't work if it's the last line in your program - it needs to stop before something else.

Once you're finished writing your method, run the program with ruby fizzbuzz.rb; the console should take you to pry, allowing you to read from (and even write to) your program. Once there, try calling your fizzbuzz method with the following arguments : 10, 15, 30, 50. Does your code work like you'd expect?

Ruby vs JS :: Collections

Arrays

Arrays in Ruby are almost identical to arrays in JavaScript, down to the square braces.

[1] pry(main)> my_array = ["a","b","c"]
=> ["a","b","c"]
[2] pry(main)> my_array[0]
=> "a"
[4] pry(main)> my_array[2] = "z"
=> "z"
[5] pry(main)> my_array
=> ["a","b","z"]

Hashes

A Ruby hash acts somewhat like a dictionary in JavaScript, in that it consists of pairs of keys and values.

[1] pry(main)> dict = {}
=> {}
[2] pry(main)> dict["a"] = 23
=> 23
[3] pry(main)> dict["a"]
=> 23

However, there are a couple of important differences. For instance, Ruby hashes do not allow you to access their keys through a dot notation; you must use square braces.

Your Turn

In pairs, edit your fizzbuzz code, adding a hash containing keys "fizz", "buzz", "fizzbuzz", and "other", each with arrays as values. As you iterate through all the numbers from 1 to max_num, add each number to one of the arrays mentioned above; numbers divisible by 3 only should go into the "fizz" array, numbers divisible by 5 only should go into the "buzz" array, numbers divisible by both should go into the "fizzbuzz" array, and numbers divisible by neither should go into the "other" array. Finally, once you're done, return the hash as the result of fizzbuzz.

Run your code from the console using ruby, and check your work using pry.

Common Gotchas When Learning Ruby After JavaScript

• == and === mean different things between the two languages. In JavaScript, === is a 'strict equality' comparator, while == is a 'loose equality' comparator; since == has some weird exceptions, the convention is to almost always use ===. In Ruby, however, the reverse is true; you should == to test for equality, and not use === (which does something different).

• Use .equal? if we need to test for identity (two variables that reference the same object).

• Ruby has several different numeric types (unlike JavaScript), but most operations "do what we expect".

• Booleans: Only false and nil are falsy in Ruby. Everything else is truthy.

• We don't need to use parentheses when invoking a method (as we saw above with the + method - one exception later). But sometimes they add clarity, so it can be beneficial to include them.

• The Ruby comment character is #. Everything following a # on a line is ignored by the interpreter.

• p, [$stdout.]puts, [$stdout.]print are not directly analogous to console.log but are often used for a similar purpose when writing scripts run from the terminal

• Ruby's convention is to use underscores between words in names (a.k.a. 'snake_case'). Constants start with a capital letter.

• Use Sublime tab completion to avoid the common, and hard to find error of writing def method_name and forgetting the closing end. Good indentation will help with this as well.

• Ruby doesn't implicitly convert numbers to strings.

Additional Resources

• Links to a variety of offical language and api documentation
• rubymonk
• why's (poignant) Guide to Ruby

License

Source code distributed under the MIT license. Text and other assets copyright General Assembly, Inc., all rights reserved.