Dart: Ruby Example

Application1.rb

 # Code Snippet for
 # Dart: A Replacement for JavaScript
 # A talk given at Twin Cities Code Camp 12
 # http://hasmanyreasons.com/2012/04/17/dart-why-you-should-care

 # The following code demonstrates how Ruby can
 # interact with multiple types with a single method
 # definition.

def first(arg)
  arg[0]
end

# Application
arg1 = [1,2,3]
arg2 = {
  :first_key => "first_val",
  :second_key => "second_val",
  :third_key => "third_val"
}
arg3 = "Test string"

puts first(arg1)
puts first(arg2)
puts first(arg3) 

# Output:
# 1
# nil
# 84

Application2.rb

 # Code Snippet for
 # Dart: A Replacement for JavaScript
 # A talk given at Twin Cities Code Camp 12
 # http://hasmanyreasons.com/2012/04/17/dart-why-you-should-care

 # This is modification of Application1.rb
 # It demonstrates how Ruby can interact with 
 # custom types with a single method definition.

def first(arg)
  arg[0]
end

class Foo

  # By defining how a Foo object responds to indexing,
  # we can determine what the return value will be
  def [](index)
    "Ruby is awesome"
  end

end

# Application
arg1 = Foo.new

puts first(arg1)

# Output:
# "Ruby is awesome"

Application3.rb

 # Code Snippet for
 # Dart: A Replacement for JavaScript
 # A talk given at Twin Cities Code Camp 12
 # http://hasmanyreasons.com/2012/04/17/dart-why-you-should-care

 # This ia modification of Application1.rb
 # In this case, we have changed the first method to have
 # a different dependency.

# Now the method definition will initially sort
# the argument, and then return the first value
def first(arg)
  arg.sort[0]
end

# Application
arg1 = [1,2,3]
arg2 = {
  :first_key => "first_val",
  :second_key => "second_val",
  :third_key => "third_val"
}
arg3 = "Test string"

puts first(arg1)
puts first(arg2)
puts first(arg3)

# Output:
# 1
# NoMethodError: undefined method `<=>' for :first_key:Symbol

# In this example, we see that while there is no
# explicit type for the first method, there are
# implicit restrictions on what it can handle.

Application4.rb

 # Code Snippet for
 # Dart: A Replacement for JavaScript
 # A talk given at Twin Cities Code Camp 12
 # http://hasmanyreasons.com/2012/04/17/dart-why-you-should-care

 # This ia modification of Application3.rb
 # Now, when we try to provide our own class,
 # we can see the challenges of defining an
 # object that will meet the implicit requirements
 # of our method.

def first(arg)
  arg.sort[0]
end

class Foo
  def [](index)
    nil
  end
  
  # The first method will call .sort on
  # our instance of Foo, so we need to
  # define a method to respond.
  def sort
    return nil
  end
end

# Application
arg1 = Foo.new

puts first(arg1)

# Output: NoMethodError: undefined method `[]' for nil:NilClass

# While we respond to sort, the return value that
# Foo provided did not respond to the [] method.
# Without any explicit warning, we have defined a
# first method that implicitly requires
# "an argument which responds to .sort with an
# object that responds to []"