wangjohn

  {{#bs-page-heading verbose=true title="Welcome back!" subtitle=(
      format-message (intl-get 'messages.dashboardOverview.subtitle')
        percentChange=(format-number averageChargePercentChange style='percent')
        previous=(format-currency previousAverageCharge currency=currency)
        current=(format-currency currentAverageCharge currency=currency)
        sign=(compute-sign averageChargePercentChange bufferedFractionDigits=2)
        timespan=(format-message (intl-get 'messages.helpers.timeElapsed')
          unitCount=(time-elapsed overviewTimespan unit='months') unit='months')
    )
  }}

wangjohn

Boston Cab Visualization

This makes a heatmap of cab pick-ups for a given time of day. You can select different ranges of time using the slider.

Questions

1. What is the message in your visualization and what techniques did you use to illustrate it?

The message in my visualization is that taxi pickup locations change depending on the time of day. It tends to be the case that in the mornings, people get picked up in Kenmore, North Station, and in Back Bay. However, in the evening, taxis tend to pick people up near the Prudential Center, the Financial District, and near South Station.

wangjohn

require 'active_support/core_ext/class/attribute.rb'
require 'benchmark'

NUM_TRIALS = 1000000

Benchmark.bm(25) do |x|
  x.report("Defining attribute") do
    NUM_TRIALS.times do
      class MyClass
        class_attribute :my_attribute

wangjohn

require 'active_model'
require 'benchmark'

class Post
  extend ActiveModel::Callbacks
  define_model_callbacks :make

  def make
    run_callbacks :make do
    end

wangjohn

module ActiveRecord
  extend ActiveSupport::Autoload

  autoload :Base
  autoload :Callbacks
  autoload :Core
  ...
end

wangjohn

activerecord/test/cases/associations_test.rb

On master (when scanning all of the callbacks):

  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
  1.85     9.26      0.82    18412     0.04     0.05  ActiveSupport::Callbacks::Callback#matches?
  1.22    12.32      0.54    18412     0.03     0.08  ActiveSupport::Callbacks::Callback#duplicates?
  0.93    14.61      0.41    19600     0.02     0.21  ActiveSupport::Callbacks::CallbackChain#remove_duplicates

wangjohn

Let's look at what happens when you do something like this inside of a view:

<%= render partial: 'some_partial' -%>

To render a partial, Rails has a helper method inside of Action View. The render method serves as a delegator and takes its input arguments and provides them to the view_renderer object.

The view_renderer object is initialized when ActionView::Base is initialized and is of the ActionView::Renderer class. This class performs all of the rendering that is necessary inside of the views. The design pattern of delegating to an object is used. When you call view_renderer.render, you are asking the view_renderer object to delegate the arguments of your call to another more specific object.

wangjohn

[Wed Apr 17 - 23:43:17]
john@ubuntu:~/taskmail
$ gem install pg

Building native extensions.  This could take a while...
ERROR:  Error installing pg:
	ERROR: Failed to build gem native extension.

    /home/john/.rvm/rubies/ruby-2.0.0-p0/bin/ruby extconf.rb
checking for pg_config... yes

wangjohn

class StrawMan
  attr_accessor :assertion_log

  @assertion_log = []

  class << self
    def check_assertions(name, &assertion)
      alias_method :some_crazy_uuid, name

wangjohn

My idea is to create something in rails where you can do checking on your rails app which is similar to statically-typed languages. When you define a method, you can specify asserts on the inputs and outputs. Imagine that @return is the return value of the method, then you could write:

#
# assert ids.all? do { |id| id.kind_of?(Integer) }
# assert @return.kind_of?(ActiveRecord)
# 
def find(*ids)
  ...
end