introduction.md

Ruby is a dynamic object-oriented language. Everything in Ruby is an object.

There are two primary ways to assign objects to names in Ruby - using variables or constants. Variables are always written in snake case. A variable can reference different objects over its lifetime. For example, my_first_variable can be defined and redefined many times using the = operator:

my_first_variable = 1
my_first_variable = "Some string"
my_first_variable = SomeComplexObject.new

Constants, however, are meant to be assigned once. They must start with capital letters and are normally written in block capitals with words separated by underscores. For example:

MY_FIRST_CONSTANT = 10

# Redefining not allowed
# MY_FIRST_CONSTANT = "Some String"

Ruby is organised into classes. Classes are defined using the class keyword followed by the name of the class. Objects are generally created by instantiating classes using the .new method. For example:

# Define the class
class Calculator
  #...
end

# Create an instance of it and assign it to a variable
my_first_calc = Calculator.new

Units of functionality are encapsulated in methods - similar to functions in other languages. A method can optionally be defined with positional arguments, and/or keyword arguments that are defined and called using the : syntax. Methods either implicitly return the result of the last evaluated statement, or can explicitly return an object via the return keyword. Methods are invoked using . syntax.

class Calculator

  # Unnamed params
  def add(num1, num2)
    return num1 + num2 # Explicit return
  end

  # Named params
  def multiply(num1:, num2:)
    num1 * num2 # Implicit return
  end
end

calc = Calculator.new
calc.add(1, 3)
calc.multiply(num1: 2, num_2: 5)