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458 lines
8.5 KiB
Markdown
458 lines
8.5 KiB
Markdown
---
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language: ruby
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filename: learnruby.rb
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contributors:
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- ["David Underwood", "http://theflyingdeveloper.com"]
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- ["Joel Walden", "http://joelwalden.net"]
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- ["Luke Holder", "http://twitter.com/lukeholder"]
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- ["Tristan Hume", "http://thume.ca/"]
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- ["Nick LaMuro", "https://github.com/NickLaMuro"]
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- ["Marcos Brizeno", "http://www.about.me/marcosbrizeno"]
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---
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```ruby
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# This is a comment
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=begin
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This is a multiline comment
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No-one uses them
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You shouldn't either
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=end
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# First and foremost: Everything is an object.
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# Numbers are objects
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3.class #=> Fixnum
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3.to_s #=> "3"
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# Some basic arithmetic
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1 + 1 #=> 2
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8 - 1 #=> 7
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10 * 2 #=> 20
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35 / 5 #=> 7
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# Arithmetic is just syntactic sugar
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# for calling a method on an object
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1.+(3) #=> 4
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10.* 5 #=> 50
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# Special values are objects
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nil # Nothing to see here
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true # truth
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false # falsehood
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nil.class #=> NilClass
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true.class #=> TrueClass
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false.class #=> FalseClass
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# Equality
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1 == 1 #=> true
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2 == 1 #=> false
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# Inequality
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1 != 1 #=> false
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2 != 1 #=> true
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!true #=> false
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!false #=> true
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# apart from false itself, nil is the only other 'falsey' value
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!nil #=> true
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!false #=> true
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!0 #=> false
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# More comparisons
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1 < 10 #=> true
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1 > 10 #=> false
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2 <= 2 #=> true
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2 >= 2 #=> true
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# Strings are objects
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'I am a string'.class #=> String
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"I am a string too".class #=> String
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placeholder = "use string interpolation"
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"I can #{placeholder} when using double quoted strings"
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#=> "I can use string interpolation when using double quoted strings"
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# print to the output
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puts "I'm printing!"
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# Variables
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x = 25 #=> 25
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x #=> 25
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# Note that assignment returns the value assigned
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# This means you can do multiple assignment:
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x = y = 10 #=> 10
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x #=> 10
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y #=> 10
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# By convention, use snake_case for variable names
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snake_case = true
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# Use descriptive variable names
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path_to_project_root = '/good/name/'
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path = '/bad/name/'
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# Symbols (are objects)
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# Symbols are immutable, reusable constants represented internally by an
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# integer value. They're often used instead of strings to efficiently convey
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# specific, meaningful values
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:pending.class #=> Symbol
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status = :pending
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status == :pending #=> true
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status == 'pending' #=> false
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status == :approved #=> false
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# Arrays
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# This is an array
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array = [1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5]
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# Arrays can contain different types of items
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[1, "hello", false] #=> [1, "hello", false]
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# Arrays can be indexed
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# From the front
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array[0] #=> 1
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array[12] #=> nil
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# Like arithmetic, [var] access
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# is just syntactic sugar
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# for calling a method [] on an object
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array.[] 0 #=> 1
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array.[] 12 #=> nil
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# From the end
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array[-1] #=> 5
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# With a start and end index
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array[2, 4] #=> [3, 4, 5]
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# Or with a range
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array[1..3] #=> [2, 3, 4]
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# Add to an array like this
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array << 6 #=> [1, 2, 3, 4, 5, 6]
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# Hashes are Ruby's primary dictionary with keys/value pairs.
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# Hashes are denoted with curly braces:
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hash = {'color' => 'green', 'number' => 5}
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hash.keys #=> ['color', 'number']
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# Hashes can be quickly looked up by key:
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hash['color'] #=> 'green'
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hash['number'] #=> 5
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# Asking a hash for a key that doesn't exist returns nil:
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hash['nothing here'] #=> nil
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# Since Ruby 1.9, there's a special syntax when using symbols as keys:
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new_hash = { defcon: 3, action: true}
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new_hash.keys #=> [:defcon, :action]
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# Tip: Both Arrays and Hashes are Enumerable
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# They share a lot of useful methods such as each, map, count, and more
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# Control structures
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if true
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"if statement"
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elsif false
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"else if, optional"
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else
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"else, also optional"
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end
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for counter in 1..5
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puts "iteration #{counter}"
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end
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#=> iteration 1
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#=> iteration 2
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#=> iteration 3
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#=> iteration 4
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#=> iteration 5
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# HOWEVER, No-one uses for loops.
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# Instead you should use the "each" method and pass it a block.
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# A block is a bunch of code that you can pass to a method like "each".
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# It is analogous to lambdas, anonymous functions or closures in other
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# programming languages.
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#
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# The "each" method of a range runs the block once for each element of the range.
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# The block is passed a counter as a parameter.
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# Calling the "each" method with a block looks like this:
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(1..5).each do |counter|
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puts "iteration #{counter}"
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end
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#=> iteration 1
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#=> iteration 2
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#=> iteration 3
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#=> iteration 4
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#=> iteration 5
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# You can also surround blocks in curly brackets:
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(1..5).each {|counter| puts "iteration #{counter}"}
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# The contents of data structures can also be iterated using each.
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array.each do |element|
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puts "#{element} is part of the array"
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end
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hash.each do |key, value|
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puts "#{key} is #{value}"
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end
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counter = 1
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while counter <= 5 do
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puts "iteration #{counter}"
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counter += 1
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end
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#=> iteration 1
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#=> iteration 2
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#=> iteration 3
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#=> iteration 4
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#=> iteration 5
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grade = 'B'
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case grade
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when 'A'
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puts "Way to go kiddo"
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when 'B'
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puts "Better luck next time"
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when 'C'
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puts "You can do better"
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when 'D'
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puts "Scraping through"
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when 'F'
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puts "You failed!"
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else
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puts "Alternative grading system, eh?"
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end
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# Functions
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def double(x)
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x * 2
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end
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# Functions (and all blocks) implicitly return the value of the last statement
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double(2) #=> 4
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# Parentheses are optional where the result is unambiguous
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double 3 #=> 6
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double double 3 #=> 12
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def sum(x,y)
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x + y
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end
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# Method arguments are separated by a comma
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sum 3, 4 #=> 7
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sum sum(3,4), 5 #=> 12
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# yield
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# All methods have an implicit, optional block parameter
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# it can be called with the 'yield' keyword
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def surround
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puts "{"
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yield
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puts "}"
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end
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surround { puts 'hello world' }
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# {
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# hello world
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# }
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# Define a class with the class keyword
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class Human
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# A class variable. It is shared by all instances of this class.
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@@species = "H. sapiens"
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# Basic initializer
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def initialize(name, age=0)
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# Assign the argument to the "name" instance variable for the instance
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@name = name
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# If no age given, we will fall back to the default in the arguments list.
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@age = age
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end
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# Basic setter method
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def name=(name)
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@name = name
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end
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# Basic getter method
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def name
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@name
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end
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# A class method uses self to distinguish from instance methods.
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# It can only be called on the class, not an instance.
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def self.say(msg)
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puts "#{msg}"
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end
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def species
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@@species
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end
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end
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# Instantiate a class
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jim = Human.new("Jim Halpert")
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dwight = Human.new("Dwight K. Schrute")
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# Let's call a couple of methods
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jim.species #=> "H. sapiens"
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jim.name #=> "Jim Halpert"
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jim.name = "Jim Halpert II" #=> "Jim Halpert II"
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jim.name #=> "Jim Halpert II"
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dwight.species #=> "H. sapiens"
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dwight.name #=> "Dwight K. Schrute"
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# Call the class method
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Human.say("Hi") #=> "Hi"
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# Variable's scopes are defined by the way we name them.
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# Variables that start with $ have global scope
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$var = "I'm a global var"
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defined? $var #=> "global-variable"
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# Variables that start with @ have instance scope
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@var = "I'm an instance var"
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defined? @var #=> "instance-variable"
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# Variables that start with @@ have class scope
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@@var = "I'm a class var"
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defined? @@var #=> "class variable"
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# Variables that start with a capital letter are constants
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Var = "I'm a constant"
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defined? Var #=> "constant"
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# Class also is object in ruby. So class can have instance variables.
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# Class variable is shared among the class and all of its descendants.
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# base class
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class Human
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@@foo = 0
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def self.foo
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@@foo
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end
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def self.foo=(value)
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@@foo = value
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end
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end
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# derived class
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class Worker < Human
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end
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Human.foo # 0
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Worker.foo # 0
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Human.foo = 2 # 2
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Worker.foo # 2
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# Class instance variable is not shared by the class's descendants.
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class Human
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@bar = 0
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def self.bar
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@bar
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end
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def self.bar=(value)
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@bar = value
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end
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end
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class Doctor < Human
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end
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Human.bar # 0
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Doctor.bar # nil
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module ModuleExample
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def foo
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'foo'
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end
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end
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# Including modules binds the methods to the object instance
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# Extending modules binds the methods to the class instance
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class Person
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include ModuleExample
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end
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class Book
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extend ModuleExample
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end
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Person.foo # => NoMethodError: undefined method `foo' for Person:Class
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Person.new.foo # => 'foo'
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Book.foo # => 'foo'
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Book.new.foo # => NoMethodError: undefined method `foo'
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# Callbacks when including and extending a module are executed
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module ConcernExample
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def self.included(base)
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base.extend(ClassMethods)
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base.send(:include, InstanceMethods)
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end
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module ClassMethods
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def bar
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'bar'
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end
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end
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module InstanceMethods
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def qux
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'qux'
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end
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end
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end
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class Something
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include ConcernExample
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end
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Something.bar # => 'bar'
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Something.qux # => NoMethodError: undefined method `qux'
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Something.new.bar # => NoMethodError: undefined method `bar'
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Something.new.qux # => 'qux'
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```
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