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---
language: ruby
author: David Underwood
author_url: http://theflyingdeveloper.com
---
```ruby
# This is a comment
=begin
This is a multiline comment
No-one uses them
You shouldn't either
=end
# First and foremost: Everything is an object.
# Numbers are objects
3.class #=> Fixnum
3.to_s #=> "3"
# Some basic arithmetic
1 + 1 #=> 2
8 - 1 #=> 7
10 * 2 #=> 20
35 / 5 #=> 7
# Special values are objects
nil # Nothing to see here
true # truth
false # falsehood
nil.class #=> NilClass
true.class #=> TrueClass
false.class #=> FalseClass
# Equality
1 == 1 #=> true
2 == 1 #=> false
# apart from false itself, nil is the only other 'falsey' value
nil == false #=> true
0 == false #=> false
# Inequality
1 != 1 #=> false
2 != 1 #=> true
!true #=> false
!false #=> true
# More comparisons
1 < 10 #=> true
1 > 10 #=> false
2 <= 2 #=> true
2 >= 2 #=> true
# Strings are objects
'I am a string'.class #=> String
"I am a string too".class #=> String
placeholder = "use string interpolation"
"I can #{placeholder} when using double quoted strings"
#=> "I can use string interpolation when using double quoted strings"
# print to the output
puts "I'm printing!"
# Variables
x = 25 #=> 25
x #=> 25
# Note that assignment returns the value assigned
# This means you can do multiple assignment:
x = y = 10 #=> 10
x #=> 10
y #=> 10
# By convention, use snake_case for variable names
snake_case = true
# Use descriptive variable names
path_to_project_root = '/good/name/'
path = '/bad/name/'
# Symbols (are objects)
# Symbols are immutable, reusable constants represented internally by an integer value
# They're often used instead of strings to efficiently convey specific, meaningful values
:pending.class #=> Symbol
status = :pending
status == :pending #=> true
status == 'pending' #=> false
status == :approved #=> false
# Arrays
# This is an array
[1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5]
# Arrays can contain different types of items
array = [1, "hello", false] #=> => [1, "hello", false]
# Arrays can be indexed
# From the front
array[0] #=> 1
array[12] #=> nil
# From the end
array[-1] #=> 5
# With a start and end index
array[2, 4] #=> [3, 4, 5]
# Or with a range
array[1..3] #=> [2, 3, 4]
# Add to an array like this
array << 6 #=> [1, 2, 3, 4, 5, 6]
# Hashes are Ruby's primary dictionary with keys/value pairs.
# Hashes are denoted with curly braces:
hash = {'color' => 'green', 'number' => 5}
hash.keys #=> ['color', 'number']
# Hashes can be quickly looked up by key:
hash['color'] #=> 'green'
hash['number'] #=> 5
# Asking a hash for a key that doesn't exist returns nil:
hash['nothing here'] #=> nil
# Iterate over hashes with the #each method:
hash.each do |k, v|
puts "#{k} is #{v}"
end
# Since Ruby 1.9, there's a special syntax when using symbols as keys:
new_hash = { defcon: 3, action: true}
new_hash.keys #=> [:defcon, :action]
# Tip: Both Arrays and Hashes are Enumerable
# This means they share a lot of useful methods such as each, map, count, and more
# Control structures
if true
"if statement"
elsif false
"else if, optional"
else
"else, also optional"
end
for counter in 1..5
puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5
# HOWEVER
# No-one uses for loops
# Use `each` instead, like this:
(1..5).each do |counter|
puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5
counter = 1
while counter <= 5 do
puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5
grade = 'B'
case grade
when 'A'
puts "Way to go kiddo"
when 'B'
puts "Better luck next time"
when 'C'
puts "You can do better"
when 'D'
puts "Scraping through"
when 'F'
puts "You failed!"
# Functions
def double(x)
x * 2
end
# Functions (and all blocks) implcitly return the value of the last statement
double(2) #=> 4
# Parentheses are optional where the result is unambiguous
double 3 #=> 6
double double 3 #=> 12
def sum(x,y)
x + y
end
# Method arguments are separated by a comma
sum 3, 4 #=> 7
sum sum(3,4), 5 #=> 12
# yield
# All methods have an implicit, optional block parameter
# it can be called with the 'yield' keyword
def surround
puts "{"
yield
puts "}"
end
surround { puts 'hello world' }
# {
# hello world
# }
```
|
