Intro to Ruby

From the Ruby Documentation

Interactive Ruby

We can use irb to run an interactive Ruby shell, when open, it will look like this:

irb(main):001:0> 

Once we've got that open, we can type a value, and the interactive shell will evaluate it

irb(main):001:0> "Hello World" 
=> "Hello World"

Though, to formally print something we can use puts like so:

irb(main):002:0> puts "Hello World" 
Hello World
=> nil

We can also see that the result of the puts command is nil which is the Ruby version of a nothing value

Math

We can do basic math using IRB as well, like so:

irb(main):004:0> 5*7
=> 35
irb(main):005:0> 5**7
=> 78125
irb(main):006:0> Math.sqrt(5)
=> 2.23606797749979
irb(main):007:0> Math.sin(0)
=> 0.0
irb(main):008:0> Math.acos(1)
=> 0.0

Methods

Defining a Method

We can define a method using def and end, so a method that prints Hello World would look like this:

def hi
  puts "Hello World"
end

Or, in the shell

irb(main):017:0> def hi
irb(main):018:1> puts "Hello World"
irb(main):019:1> end
=> :hi

Calling a Method

We can then call a method using either the name of the method, or the name followed by () if the method has no inputs

irb(main):020:0> hi
Hello World
=> nil
irb(main):021:0> hi()
Hello World
=> nil

Method Parameters

We can define hi such that it takes a name parameter like so:

def hi(name)
  puts "Hello #{name}"
end

Also note how string interpolation/templates can be done in the above string

irb(main):026:0> hi("bob")
Hello bob
=> nil

We can also call methods on an object, for example name by using either the method name with or without parenthesis as mentioned before

name.capitalize

name.capitalize()

We can then implement that in our hi method

def hi(name)
  puts "Hello #{name.capitalize}"
end

Which can be called like:

hi("bob")

or

hi "bob"

Classes

Classes are defined using the class keyword

class Greeter
  def initialize(name = "World")
    @name = name
  end

  def say_hi()
    puts "Hi #{@name}"
  end

  def say_bye()
    puts "Hi #{@name}"
  end
end

We can create an instance of the Greeter class by using Greeter.new, like so

greeter = Greeter.new("bob")

And we can then use it with:

irb(main):029:0> greeter.say_hi
Hi bob
=> nil
irb(main):030:0> greeter.say_bye
Hi bob
=> nil