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Ruby syntax 101
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| # Everything after the '#' character is a comment | |
| # Run these lines in an interactive ruby interpreter (irb) to "feel" them | |
| # Maths | |
| 9/2 == 4 | |
| 9/2.0 == 4.5 # Same as 9.0/2 or 9.0/2.0 or 9.to_f/2 | |
| 2**8 == 256 | |
| # Arrays | |
| [1, 2] + [2, 3] == [1, 2, 2, 3] | |
| [1, 2] - [2, 3] == [1] | |
| [1, 2] | [2, 3] == [1, 2, 3] | |
| [1, 2] & [2, 3] == [2] | |
| a = [] | |
| a << "toto" | |
| a == ["toto"] | |
| # Loops | |
| 10.times do |n| | |
| puts n | |
| end | |
| 10.times { |n| puts n } # oneliner syntax | |
| 1.upto(10) do |n| | |
| puts n | |
| end | |
| [1, 2, 3].each do |n| | |
| puts n | |
| end | |
| (1..10).each do |n| | |
| puts n | |
| end | |
| # Conditions | |
| # Only strongly-typed 'false' and 'nil' (ruby null equivalent) will be rejected by 'if' | |
| # While values like 0 or "" are equivalent to true | |
| condition1 = "" | |
| condition2 = false | |
| if condition1 | |
| puts "condition1 is not false nor nil" | |
| elsif condition2 | |
| puts "condition1 is false or nil, and condition2 isn't" | |
| else | |
| puts "condition1 and condition2 are both false or nil" | |
| end | |
| # Hashes | |
| # :first_name is a symbol. It's a kind of constant string used as a software internal key. | |
| # Ruby allows two different syntaxes to write hashes whose keys are symbols. | |
| { first_name: "Julien" } == { :first_name => "Julien" } | |
| { first_name: "Julien" } != { "first_name" => "Julien" } | |
| my_variable = :first_name | |
| my_hash = { first_name: "Julien" } | |
| my_hash[my_variable] == my_hash[:first_name] | |
| { first_name: "Julien" }[:first_name] # It also works without variables | |
| my_hash.each{ |key, value| puts value } # You can iterate on key-value pairs | |
| # Functions | |
| # Parentheses for parameters declaration or for function executions are optional. | |
| # If you don't use `return`, then last line of the function will be returned. | |
| def my_function | |
| 42 | |
| end | |
| my_function == 42 | |
| def my_function(i) | |
| i * 2 | |
| end | |
| my_function(10) == 20 | |
| def my_function(i: 7) | |
| i * 2 | |
| end | |
| my_function(i: 10) == 20 | |
| my_function == my_function() # 14 | |
| def my_function(i:) | |
| i * 2 | |
| end | |
| my_function(i: 10) == 20 | |
| my_function # ArgumentError (missing keyword: i) | |
| # These all return the same | |
| [1, 2, 3].map{ |i| i * 2 } | |
| ["1", "2", "3"].map(&:to_i).map{ |i| i * 2 } | |
| ["1", "2", "3"].map{ |i| i.to_i * 2 } | |
| [2, 4, 6] | |
| # Classes / Objects | |
| # @name is an instance variable. | |
| # @@thing would be a class variable, but it is rarely used. | |
| class User | |
| def initialize(name) | |
| @name = name | |
| end | |
| def greet | |
| puts "Bonjour #{@name}" | |
| end | |
| end | |
| user = User.new("Julien") | |
| user.greet == "Bonjour Julien" | |
| user.name # NoMethodError (undefined method `name' for User instance) | |
| # You can define getters and setters | |
| class User | |
| def initialize(name) | |
| @name = name | |
| end | |
| def name | |
| @name | |
| end | |
| def name=(value) | |
| @name = value | |
| end | |
| end | |
| user = User.new("Julien") | |
| user.name == "Julien" | |
| user.name = "Another name" | |
| user.name == "Another name" | |
| # Or you can use `attr_reader`, `attr_writer`, or `attr_accessor` | |
| class User | |
| attr_reader :name | |
| def initialize(name) | |
| @name = name | |
| end | |
| end | |
| user = User.new("Julien") | |
| user.name == "Julien" | |
| user.name = "Another name" # NoMethodError (undefined method `name=' for User instance) | |
| class User | |
| attr_accessor :name | |
| def initialize(name) | |
| @name = name | |
| # `self.name = name` does the same thing, thanks to `attr_accessor` | |
| end | |
| end | |
| user = User.new("Julien") | |
| user.name == "Julien" | |
| user.name = "Another name" | |
| user.name == "Another name" | |
| # About @name vs self.name: | |
| class User | |
| attr_accessor :name | |
| def initialize(name) | |
| @name = name | |
| end | |
| def greet | |
| puts "Bonjour #{self.name}" | |
| # @name and self.name memory is shared, you can mix them (but consistency is prefered!) | |
| # `self.` is mandatory for assignation (`self.name =`), | |
| # but optional for reading (`puts name` is ok). | |
| end | |
| end | |
| # Other considerations: | |
| # Undefined `@foobar` returns `nil`, while undefined `self.foobar` raises. | |
| # Some people don't like `@name` because they prefer to fail fast in case of typo. | |
| # If you don't want to expose `user.name`, you can do: | |
| # `private attr_accessor :name` | |
| # This syntax is pretty new, you won't see it in old codebase. | |
| # In Rails, @variables in controllers are accessible by the views/templates |
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