w3d5

Question 1

What is “reflection” in Ruby?

Answer 1

The ability for a program to examine itself.

Question 2

How can we use #send to call a method?

Answer 2

Use the method name as a symbol argument:

[].send(:count)

Question 3

How can we dynamically define methods?

Answer 3

With ::define_method:

class Dog
  # defines a class method that will define more methods; this is
  # called a **macro**.

  def self.makes_sound(name)
    define_method(name) { puts "#{name}!" }
  end

makes_sound(:woof)
makes_sound(:bark)
makes_sound(:grr)
end

Question 4

Are methods defined with ::define_method instance specific?

Answer 4

No

Question 5

Explain dynamic finders and how they work.

Answer 5

By overriding #method_missing, you can define an infinite number of methods:

class Cat
def say(anything)
puts anything
end

  def method_missing(method_name)
    method_name = method_name.to_s
    if method_name.start_with?("say_")
      text = method_name[("say_".length)..-1]

      say(text)
    else
      # do the usual thing when a method is missing (i.e., raise an
      # error)
      super
    end
  end
end

earl = Cat.new

earl. say_hello # puts “hello”
earl. say_goodbye # puts “goodbye”

Question 6

How can you structure a method to receive multiple types of arguments?

Answer 6

Use logic in the method to decide what to do based on the given arguments:

def perform_get(url)
if url.is_a?(Hash)
# url is actually a hash of url options, call another method
# to turn it into a string representation.
url = make_url(url)
end

  # ...
end

Question 7

What are we doing, in essence, when we initialize an instance of an object?

Answer 7

We are adding an instance variable of the new object to the instance of the class.

Question 8

How do we access all instances of a class?

Answer 8

ClassName.all

Question 9

How do we assign class variables, and why bother?

Answer 9

Use @@; this will allow inherited classes to be counted as instances of other classes:

class Dog
  def self.all
    @@dogs ||= []
  end

  def initialize(name)
    @name = name

self.class.all << self   end end

class Husky < Dog
end

h = Husky.new(“Rex”)

Dog.all # => #