• If github, airbnb and hulu can use it successfully, so can you.
• Hulu is handling almost 10M unique visitors per month
• Great for developer productivity and happiness

• MRI, YARV, Jruby, Rubinius
• Jruby and Rubinius have better thread support

• Duck Typing - An object’s type is determined by its data and methods
• Open Classes
• Meta Programming - Modify classes and methods at runtime
• Inheritance - Does not support multiple inheritance, but provides modules and mixins
• Multiple paradigms - supports multiple paradigms like oop and functional
• Automated memory management (garbage collection)

• Modules have 3 main usecases
• Namespacing
• include If you have methods that could be used in several classes, extract them to a module and include it in the classes. Each object has access to those methods. Modules may have requirements about what attributes are defined in the class
• extend Instead of the entire class, if we want only a particular object to have access to the module’s functionality we can say my_obj.extend my_module

• ruby main_file.rb - on terminal
• cmd + B- on sublime text

• Symbols are immutable

• require awesome
• File extension is not required
• Works with absolute and relative paths
• Loads the file only the first time it is encountered

• load amazing.rb
• File extension is required
• Works with absolute and relative paths
• Loads the file every single time it encounters the statement
• Does not check if the file is already loaded
• Good for exploratory code loading
• Make changes to the file and load them again in a single session

• Modules and reusable code

• For class methods

• Blocks are inspired by functional programming language Lisp. Functional programming languages encapsulate functions insdie variables, which could then be passed around and executed when needed.
• Blocks can have 2 notiations - Piece of code enclosed between { } or do end. Hash has curly braces too, but only encloses key-value pairs.
• Passed as parameter to methods, which can then execute the block anytime using the yield keyword

• Blocks can take parameters 1 for array and 2 for hash passed between the

  characters

• Procs & lambdas are ruby blocks. Instead of declaring them anonymously, we assign a proc to a variable
• Variable can then be passed to a method

• Lambda differs from the proc by requiring all the arguments to be passed correctly
• Used to define scopes in rails models

• .. - both inclusive
• ... - last element excluded

• ``` def compute_result(*param) # Do something end

compute_result(1,2,3,4) ```

• Exceptions are ruby classes
• ZeroDivisionError
• NameError - when you call a method that is not defined
• ArgumentError
• raise
• begin
• rescue - stop the errors from crashing the program. Enclosed in a begin-end block
• end
• ensure
• Rest of the code could not be executed
• catch
• throw

• Terminates the innermost

&: Operator

• Not all languages have meta programming capabilities. Example: C
• Java is catching up
• Code that writes code
• Manipulate elements in runtime. Dynamically create classes, methods and variables
• ActiveRecord makes heavy use of metaprogramming. Dynamic Finders like find_by_title do not actually exist in the codebase.
• Most classes are inherited from BasicObject Object or Kernel. Use the ancestors method
• Define method_missing ``` def method_missing method_name, *args, &block

end ``` * Math.const_get(:pi) - module method. Gets the value of the constant or a name error * Math.const_set(:pi, 3.14) - module method. Sets the value of the constant * k.send(:hello, "Warm", "Welcome") - class method. invokes the method identified by the symbol and passes it any arguments * Defining classes in runtime * Classes can be assigned to a variable * add self in the class * You can have logic inside of classe

• Struct - bundles a group of variables
• Can be used as Light weight classes
• Inherits from the Enumerable
• Structs can be used to pre determine the attributes of a class

• Set is like an array, but enforces uniqueness
• Responds to intersection, difference, merge etc

• h1 = Hash.new
• h1 = {}
• h1["author"]="matz"
• h1[:title]="ruby"
• h1.keys
• h1.values
• h1.delete(k)
• h1.has_key?(k)
• h1.has_value?(k)
• h1.flatten - converts hash to an array
• h1.to_a - converts each pair into an array
• h1.invert - reverts k & v
• h1.reject{|k,v| k <5} -
• h1.each{|k,v| v*10}

• Enumerable module provides collection classes with several traversal, search and sort methods
• The class much provide an each method which yields successive members of the collection
• If max min or sort methods are to be used, then the collection must also implement a <=> method
• all?
• any?
• none?
• one?
• map
• each_with_index
• select
• inject
• reduce