TIL, 2018-02-23, Mechanics/Koans

Musings

Tried tinkering around accessing app config. Application.get_env is different in Phoenix than from Elixir.
- Application.get_env(:my, My.Endpoint)[:title] Reference
When you edit something in config/config.exs, the server asks you to restart. It’s not like that in Rails, which causes “???” confusion.
Pattern matching: Reference Reference Reference
- Underscore if you don’t care about a part.
- You can’t have a function on the left side.
alias multiple: alias Teacher.{Repo, Post}

iex> x = 1
iex> ^x = 2 to attempt a match instead of a reassignment? # Pin operator

iex> { x, x } = { 1, 1 }
iex> { x, x } = { 1, 2 } # All references should bind to the same pattern.

# Match on starts_with

def greet("Ben" <> _) do
 IO.puts("Hello, Ben")
end

# Lists

def greet(["Ben" <> _, _last_name]) do
 IO.puts("Hello, Ben")
end

# Head/Tail

def greet([name | _]) do
 IO.puts("Hello, #{name}")
end

# Tuples

def greet({"Ben" <> _, _last_name}) do
 IO.puts("Hello, Ben")
end

# Maps. As long has map has k/v, this will work

def greet(%{first_name: name}) do
 IO.puts("Hello, #{name}")
end

Elixir Koans, 1-6.

"hello" <> "world" to concatenate.
String.contains?("Hello", "He"), trim, duplicate, upcase, reverse.
Integer.digits/1: splits to list. Integer.to_string
Integer.parse("5 years") == {5, " years"} # the un-parseable part is also returned.
Integer.parse("1.2") == {1, ".2"} # note first return in tuple is int, second is string
Float.ceil\2 # second argument decimal places to round
Float.floor
Range.new(1, 10)
Range.range?(1..10) # true
true, false, and nil are atoms. :true == true
Tuple: tuple_size, elem, insert_at, append, delete_at, to_list.
List: [a] ++ [b], [a, b] -- [a], List.wrap("value") => ["value"].

ElixirCasts, Guards

Reference

Guards: does a type check on the function argument (not all expressions are allowed, and it’s this way because they don’t want anything bad to happens while executing guards/no mutations happen anywhere).
iex> r(Shirt) to reload in memory.

def greet(name) when is_binary(name) do
 IO.puts("Hello, #{name}")
end

---

defmodule SizeTranslator do
  defguard is_small(size)  when size == 1 or size == "s" or size == "S"
end

defmodule Shirt do
  import SizeTranslator

  def colors_for(size) when is_small(size) do
    # Colors for small size
  end
end

ElixirCasts, Gravatar with Phoenix

Reference

def gravatar(email)
  email
  |> String.trim()
  |> String.downcase()
  |> :erlang.md5() # Use erlang in Elixir
  |> Base.encode16(case: :lower)

  img = "https://www.gravatar.com/avatar/#{hash}?s=150&d=identicon"
  img_tag(img)
end