pcantrell

Map and HashMap

Learning objectives:

pcantrell

# How can we harmonize the types of a Square class and a Rectangle class
# so that it's possible to write a rescale function that works on both?
#
# As we saw in class Wed, if we’re doing this in Java, inheritance cannot
# solve this problem in a simple way: both `Square extends Rectangle`
# and `Rectangle extends Square` end up violating the Liskov Substitution
# Principle. While there is a nice “is-a” relationship here — all squares
# are rectangles! — that does not translate nicely into Java’s type system.
#
# In class today, we saw that having one inherit from the other doesn’t

pcantrell

body.app-body.layout-multiple-columns.theme-mastodon-light,
body.app-body.layout-multiple-columns.theme-default,
body.app-body.layout-multiple-columns.theme-contrast {
  overflow: hidden !important;
}

body.app-body.layout-multiple-columns.theme-mastodon-light .columns-area,
body.app-body.layout-multiple-columns.theme-default .columns-area,
body.app-body.layout-multiple-columns.theme-contrast .columns-area {
  margin: 0 -1px !important;

pcantrell

Turning programmer errors into type errors

An example problem

In Wordy, suppose that BinaryExpressionNode were designed like this, with the operator modeled as a string:

public class BinaryExpressionNode extends ExpressionNode {
    // Valid operator types include "addition", "subtraction", "multiplication",
 // "division", and "exponentiation". Other strings are not valid operators.

pcantrell

1. Generalized existentials 😄 In progress!

   • Use case: implement Resource<T>, Siesta’s most obvious API design gap
   • Use case: silly dances like this

2. ✅ $0 ≠ all params

3. Fix anonymous closure argument goofiness (bug, older bug)

• Use case: I specifically made the more-frequently used closure arg the second one here so that code referencing only it as $1 would compile (where it would not if it were $0)

pcantrell

# ------ Base class with metaprogramming ------

# This might make more sense if you skip ahead to the 🦄🦄🦄🌈🌈🌈 first
# and study the desired results, then come back here.

class Animal
  def initialize(name)
    @name = name
  end

pcantrell

// Model with property observers:

Model = function() {}

Model.prototype.observe = function(prop, observer) {
    this._observers = this._observers || {}
    if(!this._observers[prop]) {
        this._observers[prop] = []
        

pcantrell

# CLOSURES IN RUBY     Paul Cantrell    http://innig.net
# Email: username "cantrell", domain name "pobox.com"

# I recommend executing this file, then reading it alongside its output.
#
# Alteratively, you can give yourself a sort of Ruby test by deleting all the comments,
# then trying to guess the output of the code!

# A closure is a block of code which meets three criteria:

pcantrell

Swift Evolution proposals for the three features I covered:

• Dynamic Member Lookup
• Dynamic Callable
• Key Path Member Lookup

Here's a good (and mildly critical) overview of dynamic member lookup.

Python interop:

• Library to use Python with normal Swift
• Plotting library I used in tonight’s demo

pcantrell

import Foundation

// WHY HAVE A TIMER SYNCED TO DISPLAY REFRESH?
// 
// Sparked by this question from Nick Lockwood:
// https://twitter.com/nicklockwood/status/1131650052701786114

class TimerPhasingSimulation
    {
    // –––––– Heart of the simulation ––––––