lecture-13/index.html at gh-pages · coreruby/lecture-13 · GitHub

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<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Introspection</title>
    <meta content="" name="description" />
    <meta content="" name="author" />
    <link href="css/reveal.css" rel="stylesheet" />
    <link href="css/simple.css" rel="stylesheet" />
    <link href="css/googlecode.css" rel="stylesheet" />
  </head>
  <body>
    <div class="reveal">
      <div class="slides"><section class="center" data-background="#000">
  <h2 class="white">
    Introspection
  </h2>
</section>
<section class="center" data-background="https://m1.behance.net/rendition/modules/65216951/disp/3a5948b5e73dff1e4b791d9cf806710e.jpg">
  <p class="fragment white">
    I'm back!
  </p>
</section>
<section class="center" data-background="https://m1.behance.net/rendition/modules/65216951/disp/3a5948b5e73dff1e4b791d9cf806710e.jpg">
  <p class="white">
    <3 Stanislav and Akseniya
  </p>
</section>
<section class="center" data-background="https://m1.behance.net/rendition/modules/65216951/disp/3a5948b5e73dff1e4b791d9cf806710e.jpg">
  <h2 class="white">
    Questions
  </h2>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">PI = 3.14

module X
  PI = 23
end

module X::Y
  p PI
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">PI = 3.14

module X
  PI = 23
end

module X:Y
  p PI
end </code></pre>
</section>
<section class="center">
  <img class="inline" src="img/troll.png" />
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">(2..Float::INFINITY).first(100).select(&:prime?) </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">(2..Float::INFINITY).lazy.map { |number| number ** 2 }.select(&:odd?).to_a </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">(2..Float::INFINITY).lazy.map { |number| number ** 2 }.select(&:odd?).first(1000) </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">def order(drink, size:, syrup: 'hazelnut')
  # ...
end </code></pre>
</section>
<section class="center">
  <p>
    What is a scope gate?
  </p>
</section>
<section class="center">
  <p>
    Which are the keywords that introduce scope gates?
  </p>
</section>
<section class="center">
  <p>
    Where are instance variables stored?
  </p>
</section>
<section class="center">
  <p>
    Where are methods stored?
  </p>
</section>
<section class="center">
  <p>
    What is a module?
  </p>
</section>
<section class="center" data-background="#F00">
  <h2 class="white">
    Introspection
  </h2>
</section>
<section class="center" data-background="#0F0">
  <h2 class="white">
    Instance Variables API
  </h2>
</section>
<section>
  <h2>
    Object#instance_variable_defined?
  </h2>
  <p>
    Returns true if the given instance variable is defined in obj
  </p>
</section>
<section>
  <h2>
    Object#instance_variable_defined?
  </h2>
  <p>
    String arguments are converted to symbols
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class Foo
  def initialize(a, b)
    @a, @b = a, b
  end
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">foo = Foo.new('answer', 42)

foo.instance_variable_defined? :@a  #=> true
foo.instance_variable_defined? '@b' #=> true
foo.instance_variable_defined? '@c' #=> false </code></pre>
</section>
<section>
  <h2>
    Object#instance_variable_get
  </h2>
  <p>
    Returns the value of the given instance variable, or nil if the instance variable is not set
  </p>
</section>
<section>
  <h2>
    Object#instance_variable_get
  </h2>
  <p>
    The @ part of the variable name should be included for regular instance variables
  </p>
</section>
<section>
  <h2>
    Object#instance_variable_get
  </h2>
  <p>
    Throws a NameError exception if the supplied symbol is not valid as an instance variable name
  </p>
</section>
<section>
  <h2>
    Object#instance_variable_get
  </h2>
  <p>
    String arguments are converted to symbols
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class Foo
  def initialize(a, b)
    @a, @b = a, b
  end
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">foo = Foo.new('answer', 42)

foo.instance_variable_get :@a  #=> 'answer'
foo.instance_variable_get '@b' #=> 42
foo.instance_variable_get '@c' #=> nil </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">foo.instance_variable_get? 'a' #=> NameError: `a' is not allowed as an instance variable name` </code></pre>
</section>
<section>
  <h2>
    Object#instance_variable_set
  </h2>
  <p>
    Sets the instance variable names by symbol to object
  </p>
</section>
<section>
  <h2>
    Object#instance_variable_set
  </h2>
  <p>
    Thereby frustrating the efforts of the class’s author to attempt to provide proper encapsulation
  </p>
</section>
<section class="center">
  <img class="inline" src="img/troll.png" />
</section>
<section>
  <h2>
    Object#instance_variable_set
  </h2>
  <p>
    The variable did not have to exist prior to this call
  </p>
</section>
<section>
  <h2>
    Object#instance_variable_set
  </h2>
  <p>
    If the instance variable name is passed as a string, that string is converted to a symbol
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class Foo
  def initialize(a, b)
    @a, @b = a, b
  end
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">foo = Foo.new('answer', 42)

foo.instance_variable_get :@a  #=> 'answer'
foo.instance_variable_get '@b' #=> 42 </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">foo = Foo.new('answer', 42)

foo.instance_variable_set @a, 'aaa'   #=> 'aaa'
foo.instance_variable_set '@b', 'bbb' #=> 'bbb'
foo.instance_variable_set '@c', 'ccc' #=> 'ccc'

foo.instance_variables                #=> [:a, :b, :c] </code></pre>
</section>
<section>
  <h2>
    Object#instance_variables
  </h2>
  <p>
    Returns an array of instance variable names for the receiver
  </p>
</section>
<section>
  <h2>
    Object#instance_variables
  </h2>
  <p>
    Note that simply defining an accessor does not create the corresponding instance variable
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class Bar
  attr_reader :a, :b
end

Bar.new.instance_variables #=> [] </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">bar = Bar.new

bar.instance_variable_set @a, 'aaa'   #=> 'aaa'
bar.instance_variable_set '@b', 'bbb' #=> 'bbb'

bar.instance_variables                #=> [:a, :b] </code></pre>
</section>
<section class="center" data-background="#0F0">
  <h2 class="white">
    Class Variables API
  </h2>
</section>
<section>
  <h2>
    Module#class_variable_defined?
  </h2>
  <p>
    Returns true if the given class variable is defined in obj
  </p>
</section>
<section>
  <h2>
    Module#class_variable_defined?
  </h2>
  <p>
    String arguments are converted to symbols
  </p>
</section>
<section>
  <h2>
    Module#class_variable_get
  </h2>
  <p>
    Returns the value of the given class variable (or throws a NameError exception)
  </p>
</section>
<section>
  <h2>
    Module#class_variable_get
  </h2>
  <p>
    The @@ part of the variable name should be included for regular class variables String arguments are converted to symbols
  </p>
</section>
<section>
  <h2>
    Module#class_variable_set
  </h2>
  <p>
    Sets the class variable names by symbol to object
  </p>
</section>
<section>
  <h2>
    Module#class_variable_set
  </h2>
  <p>
    If the class variable name is passed as a string, that string is converted to a symbol
  </p>
</section>
<section>
  <h2>
    Module#class_variables
  </h2>
  <p>
    Returns an array of the names of class variables in mod
  </p>
</section>
<section>
  <h2>
    Module#class_variables
  </h2>
  <p>
    This includes the names of class variables in any included modules, unless the inherit parameter is set to false
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class Fred
  @@foo = 99

  def foo
    @@foo
  end
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">Fred.class_variable_get :@@foo           #=> 99
Fred.class_variable_set :@@foo, 101      #=> 101
Fred.new.foo                             #=> 101
Fred.class_vriable_defined? :@@bar       #=> false </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class One
  @@var1 = 1
end

class Two < One
  @@var2 = 2
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">One.class_variables                      #=> [:@@var1]
Two.class_variables                      #=> [:@@var2, :@@var1]
Two.class_variables false                #=> [:@@var2] </code></pre>
</section>
<section class="center" data-background="#0F0">
  <h2 class="white">
    Class Variables API
  </h2>
</section>
<section>
  <h2>
    Module#const_defined?
  </h2>
  <p>
    Checks for a constant with the given name in mod
  </p>
</section>
<section>
  <h2>
    Module#const_defined?
  </h2>
  <p>
    If inherit is set, the lookup will also search the ancestors (and Object if mod is a Module)
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">Math.const_defined? "PI"         #=> true
IO.const_defined? :SYNC          #=> true
IO.const_defined? :SYNC, false   #=> false </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">Hash.const_defined? 'foobar' #=> NameError: wrong constant name foobar </code></pre>
</section>
<section data-background="http://media.giphy.com/media/U7l2ANkN9gl9e/giphy.gif"></section>
<section>
  <h2>
    Module#const_get
  </h2>
  <p>
    Checks for a constant with the given name in mod
  </p>
</section>
<section>
  <h2>
    Module#const_get
  </h2>
  <p>
    If inherit is set, the lookup will also search the ancestors (and Object if mod is a Module)
  </p>
</section>
<section>
  <h2>
    Module#const_get
  </h2>
  <p>
    The value of the constant is returned if a definition is found, otherwise a NameError is raised
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">module Foo
  class Bar
  end
end

Object.const_get 'Foo::Bar' </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">module Foo
  class Bar
    VAL = 10
  end

  class Baz < Bar; end
end

Object.const_get 'Foo::Baz::VAL'         # => 10
Object.const_get 'Foo::Baz::VAL', false  # => NameError </code></pre>
</section>
<section>
  <h2>
    Module#const_set
  </h2>
  <p>
    Sets the named constant to the given object, returning that object
  </p>
</section>
<section>
  <h2>
    Module#const_set
  </h2>
  <p>
    Creates a new constant if no constant with the given name previously existed
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">Math.const_set("HIGH_SCHOOL_PI", 22.0/7.0)   #=> 3.14285714285714
Math::HIGH_SCHOOL_PI - Math::PI              #=> 0.00126448926734968 </code></pre>
</section>
<section>
  <h2>
    Module#constants
  </h2>
  <p>
    Returns an array of the names of the constants accessible in mod
  </p>
</section>
<section>
  <h2>
    Module#constants
  </h2>
  <p>
    This includes the names of constants in any included modules (example at start of section)
  </p>
</section>
<section>
  <h2>
    Module#constants
  </h2>
  <p>
    Unless the inherit parameter is set to false
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">IO.constants.include?(:SYNC)        #=> true
IO.constants(false).include?(:SYNC) #=> false </code></pre>
</section>
<section>
  <h2>
    Module#const_missing
  </h2>
  <p>
    Invoked when a reference is made to an undefined constant in mod
  </p>
</section>
<section>
  <h2>
    Module#const_missing
  </h2>
  <p>
    It is passed a symbol for the undefined constant
  </p>
</section>
<section>
  <h2>
    Module#const_missing
  </h2>
  <p>
    Returns a value to be used for that constant.
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">def Foo.const_missing(name)
  name
end

Foo::UNDEFINED_CONST    #=> :UNDEFINED_CONST </code></pre>
</section>
<section class="center" data-background="#0F0">
  <h2 class="white">
    Methods API
  </h2>
</section>
<section>
  <h2>
    BasicObject#method_missing
  </h2>
  <p>
    Invoked by Ruby when obj is sent a message it cannot handle
  </p>
</section>
<section>
  <h2>
    BasicObject#method_missing
  </h2>
  <p>
    symbol is the symbol for the method called, and args are any arguments that were passed to it
  </p>
</section>
<section>
  <h2>
    BasicObject#method_missing
  </h2>
  <p>
    By default, the interpreter raises an error when this method is called
  </p>
</section>
<section>
  <h2>
    BasicObject#method_missing
  </h2>
  <p>
    However, it is possible to override the method to provide more dynamic behavior
  </p>
</section>
<section>
  <h2>
    BasicObject#method_missing
  </h2>
  <p>
    If it is decided that a particular method should not be handled, then super should be called, so that ancestors can pick up the missing method
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class ArrayInquirer < Array
  def method_missing(name, *args, &block)
    if name.end_with? '?'
      include? name.to_s.chomp '?'
    else
      super
    end
  end
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">munchies = ArrayInquirer.new %w(bacon ham eggs cheese)

munchies.bacon? #=> true
munchies.ham?   #=> true
muchies.spam?   #=> false </code></pre>
</section>
<section>
  <h2>
    Object#respond_to_missing?
  </h2>
  <p>
    Let us play nicely with Object#respond_to?
  </p>
</section>
<section>
  <h2>
    Object#respond_to_missing?
  </h2>
  <p>
    Hook method to return whether the obj can respond to id method or not
  </p>
</section>
<section>
  <h2>
    Object#respond_to_missing?
  </h2>
  <p>
    When the method name parameter is given as a string, the string is converted to a symbol
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class ArrayInquirer < Array
  def respond_to_missing?(name, include_private = false)
    name.end_with? '?'
  end
end </code></pre>
</section>
<section>
  <pre><code class="ruby" contenteditable="true">munchies = ArrayInquirer.new %w(bacon ham eggs cheese)

muchies.ham?                #=> true
muchies.spam?               #=> false

munchies.respond_to? :spam? #=> false </code></pre>
</section>
<section>
  <h2>
    Module#define_method
  </h2>
  <p>
    Defines an instance method in the receiver
  </p>
</section>
<section>
  <h2>
    Module#define_method
  </h2>
  <p>
    The method parameter can be a Proc, a Method or an UnboundMethod object
  </p>
</section>
<section>
  <h2>
    Module#define_method
  </h2>
  <p>
    If a block is specified, it is used as the method body
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">class SweetTalker
  define_method :say_something do |something, mood:|
    case mood
    when :happy then something.capitalize + '!'
    when :angry then 'YOU SUCK!'
    else             'meh...'
    end
  end
end </code></pre>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">person = SweetTalker.new

person.say_something 'life is good', mood: :angry    #=> "YOU SUCK!"
person.say_something 'life is good', mood: :happy    #=> "Life is good!"
person.say_something 'life is good', mood: :whatever #=> "meh..." </code></pre>
</section>
<section>
  <h2>
    Module#method_added
  </h2>
  <p>
    Invoked as a callback whenever an instance method is added to the receiver
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">module Chatty
  def self.method_added(method_name)
    puts 'Adding ' + method_name.inspect
  end
  def self.some_class_method() end
  def some_instance_method() end
end

#=> Adding :some_instance_method </code></pre>
</section>
<section>
  <h2>
    Module#method_removed
  </h2>
  <p>
    Invoked as a callback whenever an instance method is removed from the receiver
  </p>
</section>
<section class="center">
  <pre><code class="ruby" contenteditable="true">module Chatty
  def self.method_removed(method_name)
    puts "Removing " + method_name.inspect
  end

  def some_instance_method() end

  remove_method :some_instance_method
end

#=> Removing :some_instance_method </code></pre>
</section>
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