Cards

TODO: To learn about the basis of functional programming and the basic Elixir code structure

Check IDENTICON PROJECT BELOW (Elixir project)

Notes

iex -S mix inside the directory where mix.exs is there to compile and run iex
Update defp deps block to update dependencies just like Gemfile
Run mix deps.get to install the dependecies

Pattern Matching

Pattern Matching is Elixir's way for assigning a variable.
If the data structure and the no of left/right side's elements are same, then the pattern matches and assigns the variable.

Ex.)

# returns ["red"]
color1 = ["red"]

[color1] = ["red"]

return color1 #returns red

[color1, color2] = ["red", "blue"]
return color1 #returns "red"
return color2 #returns "blue"

Ex.2)

["red", color] = ["red", "blue"] -> In this case, left hard coded value must match in the right side as well.

Atoms

:some_word is the primitive data type of Elixir. Something like symbols in Ruby.

Pipe Operator

Chain method using |>

With the pipe operator, there is no need to save a variable. method after |> will use the returned result from the method before.

ExDoc

two version of a documentation.

Module Documentation

on top of the codes inside the module.

  @moduledoc """
    Provides methods for creating and handling deck of cards
  """

run mix docs: Generates docs/index.html

Function Documentation

on top of each functions

  @doc """
    Check if a card is inside the created deck

    ## Examples

      iex> deck = Cards.create_deck
      iex> Cards.contains?(deck, "Ace of Spades")
      true

  """

run mix docs: Generates docs/index.html

Testing

doctest Module will include the function documentations' examples.

Example test codes:

  test "create_deck makes 20 cards" do
    deck_length = length(Cards.create_deck)
    assert deck_length == 20
  end

  test "Shuffling a deck randomizes" do
    deck = Cards.create_deck
    refute Cards.shuffle(deck) == Cards.create_deck
  end

Two types of Data Structure in Elixir

maps

Maps are collections of key and values. Just like hashes!!

iex> colors = %{primary: "red", secondary: "blue"}
# returns %{primary: "red"}
iex> colors.primary

# Use with pattern matching
iex> %{secondary: secondary_color}  = colors
# returns blue
iex> secondary_color

Updating a map structure is confusing!!!!

colors = %{primary: "red"}

# returns an error
colors.primary = "blue"

In order to update the map, we can do it in 2 ways.

With the function
With the special syntax

Elixir provides rudimentary functions for manipulating the map. put function:

colors # returns %{primary: "red"}
colors_two = Map.put(colors, :primary, "blue")
colors_two.primary # returns blue
colors # Still returns %{primary: "red"}

# Using syntax to update original map
colors_three = %{ colors | primary: "green" }
colors_three.primary # returns green

# adding new key:value to the map
Map.put(colors, secondary_color: "green")
colors # returns # returns %{primary: "red", secondary_color: "green"}

Keyword Lists

colors = [{:primary, "red"}, {:secondary, "green"}]
colors[:primary] # returns "red"
colors = [primary: "red", secondary: "green"] # returns samething
%{primary: "red", primary: "blue"} # returns blue and not duplicate keys

Keyword list stores the duplicate keys unlike Map.

Keyword List is useful when using something like ecto. Because it can store multiple duplicate keys

When using Keyword List, when the last argument of a function is a Keyword List, [] can be removed. ex.

# This passes the keyword list as an argument to find_where function
# However, since it's the last argument of the function [] was removed,
# and since duplicate key of 'where' is used, it is a keyword list
query = User.find_where where: user.age > 10, where: user.subscribed == true

Identicon

Summary

Write a module that generates identicon(auto-generated pixel image), which will return images based on the string inputs.

Identicon requires 5 x 5 grid, 250px x 250px with each square being 50px. Colors will be automatically filled and will always be identical or symmetric about the center.

Requirements

Elixir

Check identicon directory in the repository.

Algorithm

String input
Compute MD5 hash of string
List of numbers based on the string
Pick color
Build grid squares
Convert grid into image
Save image as a file

91juhwang / elixir-udemy