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Definition

Ruby is a dynamic, interpreted, reflective, object-oriented, general-purpose programming language developed in the mid-1990s by Yukihiro Matsumoto in Japan.

#: hello beer: drink 0.5 liter in 4 rounds

LITER_PER_SIP = 37e-3

def sips2liter( num_sips )
    num_sips * LITER_PER_SIP
end

beer_l = 0.5
rounds = 4
sips_per_round = [3, 7, 4, 2]

puts "I drink #{beer_l} l in #{rounds} rounds:"
sips_per_round.each do |sips|
    puts "I drink #{sips} sips."
    sleep sips 
    beer_l -= sips2liter( sips )
    if beer_l <= 0.0
        puts "My beer is empty!"
        break
    else
        puts "I have #{beer_l} l beer left."
    end
end

Important Basics

Data Types

The basic data types are Number, String, Symbol, Hash, Array, Boolean. Strings are mutable; Symbols are not.

Strings

ss = 'This is a single-quoted string'
ss = %q{This is a single-quoted string}

ds = "\nThis is a double-quoted string\n"
ds = %Q{\nThis is a double-quoted string\n}
ds = %{\nThis is a double-quoted string\n}

Strings support variable interpolation:

var = 3.14159
"pi is #{var}"   # will print "pi is 3.14159"

Collections

There are two collection types: Array and Hash

array = [1, 'hi', 3.14, 1, 2, [4, 5]] 
array.each {|item| puts item }   # iterate and print

hash = { :water => 'wet', :fire => 'hot' }

Classes

Class Variables

There are four types of variables:

  1. $globalvar: global variables, which can be accessed on the whole file
  2. @@classvar: class variables, which have the same value across all class instances (i.e. static variables).
  3. @instancevar: instance variables, which have different values for each object instance.
  4. localvar: local variables, which are only valid within one function.
$company = 'AwesomeComp'     # global variable
class Employee
    @@num_employees = 0      # Shared between class and subclasses
    @name = 'Alice'          # Specific to this instance

    def initialize
        @@num_employees += 1
        puts "Number of employees created = #{@@num_employees}"
    end
end

Exceptions

begin
  # do something
rescue Exception, RuntimeError
  # handle exception (multible can match)
else
  # do this if no exception was raised
ensure
  # do this whether or not an exception was raised
end

References