The followings are expressions:

• Class definition
• Method definition
• if statement

The followings are expressions:

• Class definition
• Method definition
• if statement expression

Valid, but don't do this:

p(if (class C; self; end)
  def f a=(def g a; 'g'; end)
    g a
  end
  g f
end) # => 'g'

The followings are objects:

• Class
• Method
• TOPLEVEL_BINDING

There's more than one
way to do it (perlish)

Object.instance_method(:p).bind(self).call(self)
# => main

p self # => main

Today's Topics:

• Type System
• Static Typing vs Dynamic Typing
• Strong or Weak? Coercion?
• Runtime System (Object Model)
• Object is an Object itself
• Singleton Pattern? Class?
• Muack -- Yet Another Mocking Library

Today's Topics:

• Type System
• Static Typing vs Dynamic Typing
• Strong or Weak? Coercion?
• Runtime System (Object Model)
• Object is an Object itself
• Singleton Pattern? Class?
• Muack -- Yet Another Mocking Library

Static Typing vs
Dynamic Typing

• They are not conflicting
• Think of DT as "unityped" in ST
  • ref: Dynamic languages are static languages
• Downcasting is dynamic type checking

Extracted from gson

@SuppressWarnings("unchecked")
public <T> T fromJson(String json, Type typeOfT) throws JsonSyntaxException {
  if (json == null) {
    return null;
  }
  StringReader reader = new StringReader(json);
  T target = (T) fromJson(reader, typeOfT);
  return target;
}

Duck Typing

Duck.new.walk

Object duck = new Duck();
if(duck.isRespondingTo("walk"))
    duck.dispatch("walk");
else
    throw new NoMethodError(duck, "walk");

Today's Topics:

• Type System
• Static Typing vs Dynamic Typing
• Strong or Weak? Coercion?
• Runtime System (Object Model)
• Object is an Object itself
• Singleton Pattern? Class?
• Muack -- Yet Another Mocking Library

Strong or Weak? Coercion?

• Vague terms
• It's not about static typing or dynamic typing
• Sometimes it means implicit type coercion

Perl Type Coercion

'1' +  1  #   2
 1  . '1' # '11'

'1' +  1     // '11'
 1  + '1'    // '11'
 true + true //   2
 true + []   // 'true'

More
JavaScript Type Nonsense

true + null      // 1
true + undefined // NaN
true + {}        // 'true[object Object]'
new Date(0) + 0  // 'Thu Jan 01 1970 08:00:00 GMT+0800 (CST)0'
new Date(0) - 0  // 0

Today's Topics:

• Type System
• Static Typing vs Dynamic Typing
• Strong or Weak? Coercion?
• Runtime System (Object Model)
• Object is an Object itself
• Singleton Pattern? Class?
• Muack -- Yet Another Mocking Library

Object is an Object itself?

Object.kind_of?(Object)   # true

Object instanceof Object // ?

If A is a kind of B...
B must either be:

#    A's class
     B ==      A.class
# or A's class' superclass
     B ==      A.class.superclass
# or A's class' superclass' superclass
     B ==      A.class.superclass.superclass
# or A's class' superclass' superclass' superclass
     B ==      A.class.superclass.superclass.superclass
# ...

Assume A and B
are both Objects...

#    A's class
     B ==      A.class
# or A's class' superclass
     B ==      A.class.superclass
# or A's class' superclass' superclass
     B ==      A.class.superclass.superclass
# or A's class' superclass' superclass' superclass
     B ==      A.class.superclass.superclass.superclass
# ...

Assume A and B
are both Objects...

# =>      v Class
Object == Object.class
# or A's class' superclass
     B ==      A.class.superclass
# or A's class' superclass' superclass
     B ==      A.class.superclass.superclass
# or A's class' superclass' superclass' superclass
     B ==      A.class.superclass.superclass.superclass
# ...

Assume A and B
are both Objects...

# =>      v Class
Object == Object.class
# =>      v Module
Object == Object.class.superclass
# or A's class' superclass' superclass
     B ==      A.class.superclass.superclass
# or A's class' superclass' superclass' superclass
     B ==      A.class.superclass.superclass.superclass
# ...

Assume A and B
are both Objects...

# =>      v Class
Object == Object.class
# =>      v Module
Object == Object.class.superclass
# =>      v Object
Object == Object.class.superclass.superclass
# or A's class' superclass' superclass' superclass
     B ==      A.class.superclass.superclass.superclass
# ...

Assume A and B
are both Objects...

# =>      v Class
Object == Object.class
# =>      v Module
Object == Object.class.superclass
# =>      v Object
Object == Object.class.superclass.superclass
# =>      v BasicObject
Object == Object.class.superclass.superclass.superclass
# ...

Thus:

Object.new.kind_of?(Object) # true
# because
Object == Object.new.class

Object    .kind_of?(Object) # true
# because
Object == Object    .class.superclass.superclass

Cool facts:
Class/Module is also a Class/Module itself

 Class.kind_of?(Class ) # => true
# because
 Class.class            # => Class
# thus
 Class ==  Class.class

Cool facts:
Class/Module is also a Class/Module itself

Module.kind_of?(Module) # => true
# because
Module.class            # => Class
# thus
Module == Module.class.superclass

Today's Topics:

• Type System
• Static Typing vs Dynamic Typing
• Strong or Weak? Coercion?
• Runtime System (Object Model)
• Object is an Object itself
• Singleton Pattern? Class?
• Muack -- Yet Another Mocking Library

Singleton Pattern

require 'singleton'
class Mario
  include Singleton


  def greets
    puts "It's me, Mario!"
  end
end
Mario.instance.greets

Singleton Pattern Underneath

# (simplified)
class Mario
  def self.instance
    @instance ||= new
  end
  def greets
    puts "It's me, Mario!"
  end
end
Mario.instance.greets

Singleton Pattern *Simplest*

Mario = Object.new



  def Mario.greets
    puts "It's me, Mario!"
  end

Mario.greets

Introducing Singleton Class

Also called
Metaclass (Smalltalk) or
Eigenclass

Mario.singleton_class
# => #<Class:#<Object:0xDEADBEEF>>

Introducing Singleton Class

Also called
Metaclass (Smalltalk) or
Eigenclass

• An instance's method is defined in a class
• In its direct class, or
• In one of its direct class' superclasses, or
• In its singleton_class

An instance's method is defined in its
singleton_class

If and only if

The other instances of the same class do not have the same method

Mario is an Object

Mario = Object.new



  def Mario.greets
    puts "It's me, Mario!"
  end

Mario.greets

The other Objects do not greet

# ...like a Mario!







# NoMethodError: undefined method `greets'
Object.new.greets

So class methods are
singleton methods!

.

Remember?

An instance's method is defined in its
singleton_class

If and only if

The other instances of the same class do not have the same method

Time is an instance of Class,
But the other Classes
Do not have this method:

Time.at(0)

The other instances of the same class do not have the same method

So class methods are
singleton methods!

Time.class # => Class
Time.at(0) # => 1970-01-01 08:00:00 +0800
Hash.class # => Class
Hash.at(0) # => NoMethodError: undefined method

Time.at is defined in Time's singleton class.
The same as Mario.greet

So class methods are
singleton methods!

  def Mario.greet; puts "It's me, Mario!"; end
Mario.singleton_class.module_eval do
  def       greet; puts "It's me, Mario!"; end
end

Time.at is defined in Time's singleton class.
The same as Mario.greet

Don't get confused.

Ruby's singleton class

Has nothing to do with

Singleton pattern.

...It's eigenclass after all

If

We need to go deeper

For Method Dispatching

Today's Topics:

• Type System
• Static Typing vs Dynamic Typing
• Strong or Weak? Coercion?
• Runtime System (Object Model)
• Object is an Object itself
• Singleton Pattern? Class?
• Muack -- Yet Another Mocking Library

A taste of Muack

require 'muack'
include Muack::API
Mario = 'Mario'
mock(Mario).greet{ "It's me, #{Mario.reverse}!" }
mock(Mario).reverse.proxy.returns(&:reverse)
puts Mario.greet # "It's me, Mario!"
Muack.verify

• greet and reverse is defined in Mario's singleton class
• Proxy would call super to call the original method

any_instance_of

Luigi = Class.new{
           def greet; "It's me, #{self}!" end }
any_instance_of(Luigi) do |luigi|
  mock(luigi).to_s.proxy.returns{ |s| s[/\w+/] }
end
puts Luigi.new.greet # It's me, Luigi!
Muack.verify

• greet and to_s is defined in Luigi (not singleton class)
• Proxy would call super to call the original method

Trick in AnyInstanceOf:

Muack::AnyInstanceOf =
  Class.new(Struct.new(:singleton_class))

Muack::AnyInstanceOf.new(Luigi).
  singleton_class == Luigi # true

If

We need to go deeper

For Muack

Use the Source, Tux!