westmichiganrubytraining/discover_ruby

A brief tutorial to help a total newcomer discover the wonders of Ruby

Discover Ruby!

If you have Ruby installed on your computer, open a terminal window and type irb. A special session will start that allows you to type any Ruby code you want and see the results immediately!

If you don't have Ruby installed or aren't yet comfortable with the command line, check out REPL.it which lets you type Ruby code in the left window and see the results on the right. Be warned, repl.it uses an old version of Ruby, so not all the newest tricks will work, but everything in this guide will be fine.

Start Exploring

So, whichever way you've chosen to try Ruby, there's a blank screen staring back at you, waiting for you to give it instructions. What sorts of instructions are there? The rest of this post gives you things to try out in Ruby, grouped by tasks and ideas you might have, like "lists" and "transforming" and the difference between a recipe and a meal.

Feel free to try things. It's completely safe: you can't break your computer. Exploring is the best way to learn. It's also a lot of fun!

Buckets with labels (aka "variables")

his_name   = "Miles"
her_name   = "Ella"
a_number   = 1
some_words = "three blind mice"
an_array   = [ 1, 2, 3 ] # see "Arrays", below

Variables are labeled buckets that carry around whatever you put to the right of the equal sign. You'll see below that when we use the variable name (the "label"), we get back whatever we put inside it. Ask for the bucket, you get what's in it.

Display (aka "output")

puts "Hello World!" # displays "Hello World!" on the screen on its own line
print "the" # displays "the"
puts "ater" # displays "theater", because previous print didn't finish with a linebreak
puts "His name is: #{his_name}" # displays "His name is: Miles"
puts "#{his_name} is friends with #{her_name}" # displays "Miles is friends with Ella"

In this guide, we show you the result of the code snippets by magic, but to see anything in your terminal, you need to display it somehow. puts (short for "put string") is the most common, but print and p have their uses, as well. Try them out and see how they differ. (Hint: maybe on an array?)

The weird #{his_name} thing is a way to say "put the contents of this bucket here in my output", so the output will contain "Miles" or "Ella".

Choices (aka conditionals)

if (a == 1)
  "one"
elsif (a < 5)
  "a few"
else
  "lots"
end

a = 1  # => "one"
a = 2  # => "a few"
a = 10 # => "lots"

We don't always know in advance what the program will need to do, so we use "conditionals" to handle multiple possibilities. The important detail is that the first conditional that matches the situation "wins" and its code will run. Nothing afterward will be run. If nothing matches, the program does nothing and continues on as if nothing happened. The else clause catches everything, so make sure you put it last. ;-)

Note that a == 1 has a pair of equal signs. One equal sign means "put this in the bucket" but a pair asks "does what's in the bucket match the thing on the right side? Yes or no".

Lists (aka Arrays)

ary = [ "one", "two", "three" ]

ary[0]    # => "one"
ary[1]    # => "two"
ary.first # => "one"
ary.last  # => "three"
ary << "four"
ary       # => [ "one", "two", "three", "four" ]

Fun Fact: we get the first item in the list with the number zero because arrays need to know how far from the beginning of the list your item is. The first item is zero items away from the beginning of the array. The second is one item from the beginning. Weird, I know, but virtually all programming languages do it this way, so we can't complain too loud. ;-)

The ary.first and ary.last are method calls, which we will see more of in a minute. Arrays are objects which respond to certain commands. Later on we'll be creating our own objects and our own commands.

Named Groups (aka Hashes)

miles = { "name" => "Miles Davis" }
ella = { "name" => "Ella Fitzgerald" }
miles["name"] # => "Miles Davis"
miles["address"] = "1234 Cool St." # let's add another pair!
miles.keys # => [ "name", "address" ]
miles.values # => [ "Miles Davis", "1234 Cool St." ]

friends = [ miles, ella ]
friends[0]["name"] # => "Miles Davis"
friends.last["name"] # => "Ella Fitzgerald"

Hashes are great when we have data we need to look up, like finding someone's phone number when all you know is their name. We don't care who's first or last, so an array can't help us. These "name-value pairs" can be really handy for making things like phone books or dictionaries, as shown below.

phone_book = { "miles" => "616-555-1212", "ella" => "616-555-1234" }
dictionary = {
  "Ruby" => "Ruby is an awesome programming language",
  "Python" => "Python is an excellent choice, too"
}
phone_book["miles"] # => "616-555-1212"

They get really powerful when you start putting them inside arrays or even inside other hashes, but we'll let you explore that yourself. :-)

Walking a list (aka "iteration")

ary = [ 1, 2, 3 ]
ary.each do |item|
  puts item
end

It's often handy to do something with each item in an array, so arrays have a method called each to do just that. It walks through the array in order and hands you a single item in a variable found between the "pipe" characters. (You'll have to hunt for the "pipe" key on your keyboard, but it's there!) In this case, the variable is called item.

This code will output the three numbers in the array, one to a line. This task is much uglier in many other languages, so this is a popular feature in Ruby. :-)

Transforming (aka Mapping, Selecting, Reducing)

nums = [ 1, 2, 3 ]
nums.map{ |num| num * 2 } # => [ 2, 4, 6 ]
names = [ "miles", "ella" ]
names.map{ |name| name.upcase } # => [ "MILES", "ELLA" ]

nums.select{ |num| num > 2 } # => [ 3 ]
nums.select{ |num| num.odd? } # => [ 1, 3 ]

nums.reduce{ |sum,num| sum + num } # => 6

nums.map{ |num| num * 2 }.reduce{ |sum,num| sum + num } # => 12

A surprising amount of programming involves "doing something" with a bunch of data (typically in an array), and these are the big three tasks: we can change each piece of data with a map, filter to just the items we're interested in with a select and/or combine them into a single thing with a reduce.

All three of these tools are in a module called Enumerable and there are many others. I like to say that 75% of what's cool in Ruby is in Enumerable, so check it out for yourself!

Jobs (aka "methods")

def speak words
  puts words
end

def double_it num
  num * 2
end

speak("Hello World!") # displays "Hello World!" on the screen
speak("Ruby is awesome!") # displays "Ruby is awesome!" on the screen
puts double_it(3) # displays 6 on the screen
speak(double_it(3)) # also displays 6!

Sometimes we have certain jobs we want to do again and again, maybe with small differences each time. To keep from having to write the code again and again, we "define" a chunk of code called a "method" using the def command followed by the name of the method and a list of variables (aka "arguments") the methods needs (if there are any) separated by commas. We put end after the code so Ruby knows where the method ends. (You probably guessed that)

In our example, we define a method called speak that takes one argument called words. It uses puts to output the contents of the words argument and then ends. Ruby goes back to where you called speak and continues running the rest of your code.

Methods can return information, too. In fact, they always do, but sometimes we ignore the info if it's nothing important. The double_it method's job is to double the number you give it and give the doubled number back to you.

In some languages, you have to return a value explicitly, but Ruby automatically returns the value of the last bit of code it executes. In the case of double_it the last thing was calculating the value of num * 2, so Ruby returns 6!

The last line of the example shows that you can pass the results of one method to another method (in this case, the results of double_it go to speak). This can be a bit hard to read, because Ruby digs down into the deepest set of parentheses and executes that first, then pops out to the next level and executes that, etc. So to understand the code you read it "inside out".

This is how Ruby executes that last line:

• 3 # => 3
• double_it(3) # => 6
• speak(6) # displays 6 on screen

Recipes and Meals (aka Classes and Objects)

class Greeter
  def initialize(greeting)
    @greeting = greeting
  end

  def greet(name)
    puts "#{@greeting} #{name}"
  end
end

cowboy  = Greeter.new("howdy")
hipster = Greeter.new("yo")
cowboy.greet("Miles") # "howdy Miles"
hipster.greet("Ella") # "yo Ella"

You can't eat a recipe, but you can make a meal by following its instructions. We call our recipes classes and the meals they make objects. In our example we put the instructions inside of a class named Greeter. Notice the end at the bottom, so Ruby knows where your recipe ends: just like a method!

We tell Ruby to "make a meal" by using the name of the class followed by a call to the new method (which is given to us free by Ruby: we don't need to write it ourselves). Anything we hand to new (in this case, "howdy" and "yo") get passed along to the initialize method, which Ruby calls itself when it's completed all the hidden tasks required to make a new object.

Why does Ruby need new and initialize?

new is a method Ruby automatically gives to every class, including the ones you define. new knows how to do all the behind-the-scenes work needed to create an object. The last thing new does is call the initialize method in your class (if you defined one) and passes along the arguments you gave it (if you supplied any). initialize is where you put any code that customizes each individual object, allowing them to act differently. In our example, we give different greetings to the cowboy and hipster objects, allowing them to respond differently to the greet method.

We put this new object in a bucket with a useful ("intention-revealing") name so we can give it orders later on.

But there are two methods defined inside Greeter! The other one is greet and it gets copied into every object, so all the objects we create can use it. This is true of every method you define within your class: initialize is the exception. There are other kinds of methods to discover on your own: try googling ruby class method and see what you find.

One other weird bit is that @greeting = greeting thing. Why are we assigning the contents of greeting to itself? That @ sign is important: that makes it a variable that lives only inside the object, invisible to the outside world. However, the greet method lives inside the object too, so it can see and use @greeting, as demonstrated on the puts line.

You've begun your adventure!

There are lots of places you can go with Ruby now that you've gotten some of the basics under your belt. May I humbly recommend 7 Degrees of FizzBuzz? You have almost all the info you need to do the first few steps of the challenge, though you'll want to investigate either Range or .upto to get going. There are many other useful resources on the site as well, so check it out!

Exploring and discovering new things on your own will be part of your daily life as a programmer, so embrace it and find the joy in finding things out.

Best of luck. I believe in you!