jayzz55

9: Designing Cost-Effective Tests

3 Skills Needed to Write Changeable Code

• Understand OO design
• Skilled at refactoring code
• Ability to write high-value tests

Changeability is the only design metric that matters; code that's easy to change is well-designed.

>Good design preserves maximum flexibility at minimum by putting off decisions at every opportunity, deferring commitments until more specific requirements arrive. When that day comes, refactoring is how you morph the current code structure into the one what will accommodate the new requirements.

jayzz55

2: Performing Work

Sending a strong message

The foundation of an object oriented system is the message.

Strong and confident messages requires three elements:

1. We must identify the messages we want to send in order to accomplish the task at hand.
2. We must identify the roles which correspond to those messages.
3. We must ensure the method's logic receives objects which can play those

jayzz55

F[A]                Ordering[Int]
B => A              listing => listing.id
F[B]                Ordering[Listing]

val intOrderer: Ordering[Int]
val listingOrderer: Ordering[Listing] = intOrderer.contraMap(listing => listing.id)

See: http://igstan.ro/posts/2013-10-31-contravariant-functors-an-intuition.html

jayzz55

# Signal catching
def shut_down
  puts "\nShutting down gracefully..."
  sleep 1
end

puts "I have PID #{Process.pid}"

# Trap ^C 
Signal.trap("INT") { 

jayzz55

# Phoenix
if grep -q '^  "phoenix"' mix.lock; then
  source $HOME/.asdf/asdf.sh
  source $HOME/.asdf/completions/asdf.bash
  export $(cat $RELEASE_DIR/../../.rbenv-vars | xargs)

  echo '
-----> Detected Phoenix app.'
  mix local.rebar --force
  mix local.hex --force