Elixir Tips

It is a great pleasure to come up with another set of tips that you may or may not know. I am using 👇

Erlang/OTP 22 [erts-10.6.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]

Elixir 1.10.0 (compiled with Erlang/OTP 21)

1. Elixir’s Ebin Directory

iex> elixir_ebin_path = :code.lib_dir(:elixir, :ebin)

What this for ?

We can find all the protocols available for us by using elixir_ebin_path .

iex> elixir_ebin_path = :code.lib_dir(:elixir, :ebin)
iex> Protocol.extract_protocols([elixir_ebin_path])

2. Finding Protocol implementations

We can easily find whether a protocol is implemented for particular type using the protocol .

Let’s check our Enumerable protocol is implemented for bitstring or not.

iex> Enumerable.impl_for(<<>>)
nil

The output for the expression is nil which indicates the Enumerable protocol is not implemented for BitString type if it has implemented, it would give the ModuleName. Check below 👇

iex> Enumerable.impl_for(%{})
Enumerable.Map
iex> Enumerable.impl_for(1..2)
Enumerable.Range

You can pass any valid structure to know the protocol implementations.

Listing All implementations of a Protocol

iex> Enumerable.__protocol__(:impls)
{:consolidated,[Map, HashSet, Date.Range, Function, File.Stream, 
GenEvent.Stream, HashDict,List, Range, Stream, MapSet, IO.Stream]}

In the same way you can get more info using the following functions

def __protocol__(:module)
def __protocol__(:functions)
def __protocol__(:consolidated?)
def __protocol__(:impls)

3. Compile Time Search Patterns over Strings or Binaries

The Big string operations might be time taking ones. For an example splitting a big string.

We can build compile time search patterns using :binary.compile_pattern.

This pattern can later be used in run time for splitting a string or any relevant operations over string or binary.

In one sentence, it is ready by the time it is compiled.

iex> pattern = :binary.compile_pattern("@")
{:bm, #Reference<0.1776527838.1813905411.150152>}

iex> [user, host] = String.split("[email protected]", pattern)
["john", "blackode.in"]

You can also give list of binaries for :binary.compile_pattern where each one is alternative for searching patterns.

iex> pattern = :binary.compile_pattern(["@", "#"])
{:bm, #Reference<0.1776527838.1813905411.150152>}
iex> [user, host, blog] = String.split("john@blackode#medium", pattern)
["john", "blackode", ,"medium"]

4.Compiling Files to the specific Path

We can compile Elixir files to the specific path, and we can run those files from their compiled directory as it contains respective beam_files.

Assume that I have three .ex files hello.ex, shop.ex, & rates.ex in my present code directory ~/mycode/elixir .

Now, I run iex from my ~/mycode/elixir directory and I try to compile files to some other directory named as ~/mycode/elixir/beamfiles

#~/mycode/elixir
iex> files = ~w(hello.ex shop.ex rates.ex)
["hello.ex", "shop.ex", "rates.ex"]
iex> Kernel.ParallelCompiler.compile_to_path files, "beamfiles"
{:ok, [Hello, Rates, Shop], []}

Now, I change my directory to ~/mycode/elxir/beamfiles and try to run iex and execute functions from compiled modules [Hello, Rates, Shop].

Check them live here

5. Finding Package Retirements

mix hex.audit

I hope you haven’t run this in any of your projects before. If you did, then a round of applause for you.

What it does ?

It looks for all the dependencies inside your dependency tree and checks for any of these has retired.

Who needs it?

Package Retirement is very important for package owners or package maintainers if they do care about their users to warn them about package security issues, it’s working condition on that version number, it’s compiling status, major bug issues, etc… like and so.

If no retired packages found, then it replies with No retired packages found.

Similarly, you can also run mix hex.outdated It does what it sounds alike.

6. Finding a whether function is a Built-In or Not

This relates to Erlang

iex> :erlang.is_builtin(:erlang, :>, 2)
true

You have to provide a Module, Function, and Arity.

7. Number Comparison in Guard Clause

Always combine comparisons with is_number()

Why?

defmodule Bank do
   def credit(amount) when amount > 0 do
      #code
   end
end

The above function use the guard amount > 0 what if we send nil , it still evaluates to true.

At production grade coding, one has to be cautious. We can’t risk on number especially on floats. The math on floats is harder.

So, go for

defmodule Bank do
  def credit(amount) when is_number (amount) and amount > 0 do

      #code
 
  end
end

8. Empty map pattern matching function

As we all know that %{} matches any kind of map. So, we cannot simply pattern match it like def hello(%{}) as it matches any map. If you want to match an empty map %{} in a function, you have to use a guard clause.

defmodule Hello do
  def hello(map) when map == %{} do
    IO.puts "I am hungry! My stomatch is empty"
  end
  def hello(map) do
    IO.puts "I am done! My stomach is full"
  end
end

You can also take the help of Kernel.map_size/1 as it is allowed in guard clause.

def hello(map) when map_size(map) == 0 do

9. Converting String to Atom

This may look easy but suppose you don’t know whether the value you are getting is atom or string but you need to extract that key from a map which has keys as atoms where you have to convert the given value to atom if it is a binary.

As we are having doubt on the received value whether it is atom or string, we force convert that to an atom using String.to_atom/1. It works for strings but if we try to convert atom to atom using String.to_atom/1 then we will get an exception.

So, we use same function with a different style with string interpolation.

cart = %{ price: 2345, tax: 100}
key1 = "price"
key2 = :price

Now, we have to extract the price using above keys.

def get_from_cart(cart, key) do
  Map.get(cart, key)
end

The above function works only when key is atom. Let’s check that

Sol 1: Using String Interpolation

def get_from_cart(cart, key) do
  key = String.to_atom("#{key}")
  Map.get(cart, key)
end

Sol: 2 Using Guard clause when

def get_from_cart(cart, key) when is_binary(key) do
  key = String.to_atom(key) 
  Map.get(cart, key)
end
def get_from_cart(cart, key) do
  Map.get(cart, key)
end

In Sol:1 we are converting every time, while in Sol:2 we are using guard to convert to atom or not.

10. Sorting Dates Improvement(elixir v 1.10)

No more hassle to sort dates now.

Before elixir v 1.10, we have to pass another function for proper sorting of dates like in the following way…

iex> Enum.sort([~D[2019-12-31], ~D[2020-01-01]], &(Date.compare(&1, &2) != :lt))
[~D[2019-12-31], ~D[2020-01-01]]

Now in elixir v 1.10, you can do it as follows

iex> Enum.sort([~D[2019-12-31], ~D[2020-01-01]], Date)
[~D[2019-12-31], ~D[2020-01-01]]
iex> Enum.sort([~D[2019-12-31], ~D[2020-01-01]], {:desc, Date})
[~D[2020-01-01], ~D[2019-12-31]]

The above examples are directly copied from original documentation.

🎉 Happy Coding :)

WRITTEN BY

Blackode

10 Killer Elixir Tips —#10