Killer Elixir-Tips

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Elixir Tips and Tricks from the Experience of Development. Each part consists of 10 Unique Tips and Tricks with a clear explanation with live examples and outputs. These tips will speed up your development and save you time in typing code as well.

You can read specific parts with following links...

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All Photos by Form on Unsplash​

Checkout some cherry picked tips from the all Parts

Taste Before you Eat :)

iex Custom Configuration - iex Decoration

Copy the content into a file and save the file as .iex.exs in your ~ home directory and see the magic. You can also download the file HERE​

# IEx.configure colors: [enabled: true]
# IEx.configure colors: [ eval_result: [ :cyan, :bright ] ]
IO.puts IO.ANSI.red_background() <> IO.ANSI.white() <> " ❄❄❄ Good Luck with Elixir ❄❄❄ " <> IO.ANSI.reset
Application.put_env(:elixir, :ansi_enabled, true)
IEx.configure(
 colors: [
   eval_result: [:green, :bright] ,
   eval_error: [[:red,:bright,"Bug Bug ..!!"]],
   eval_info: [:yellow, :bright ],
 ],
 default_prompt: [
   "\e[G",    # ANSI CHA, move cursor to column 1
    :white,
    "I",
    :red,
    "❤" ,       # plain string
    :green,
    "%prefix",:white,"|",
     :blue,
     "%counter",
     :white,
     "|",
    :red,
    "▶" ,         # plain string
    :white,
    "▶▶"  ,       # plain string
      # ❤ ❤-»" ,  # plain string
    :reset
  ] |> IO.ANSI.format |> IO.chardata_to_string
​
)

Creating Custom Sigils and Documenting

Each x sigil calls its respective sigil_x definition

Defining Custom Sigils

defmodule MySigils do
  #returns the downcasing string if option l is given then returns the list of downcase letters
  def sigil_l(string,[]), do: String.downcase(string)
  def sigil_l(string,[?l]), do: String.downcase(string) |> String.graphemes
​
  #returns the upcasing string if option l is given then returns the list of downcase letters
  def sigil_u(string,[]), do: String.upcase(string)
  def sigil_u(string,[?l]), do: String.upcase(string) |> String.graphemes
end

usage

Load the module into iex

iex> import MySigils
iex> ~l/HELLO/
"hello"
iex> ~l/HELLO/l
["h", "e", "l", "l", "o"]
iex> ~u/hello/
"HELLO"
iex> ~u/hello/l
["H", "E", "L", "L", "O"]

Custom Error Definitions

Define Custom Error

defmodule BugError do
   defexception message: "BUG BUG .." # message is the default
end

Usage

iex bug_error.ex
​
iex> raise BugError
** (BugError) BUG BUG ..
iex> raise BugError, message: "I am Bug.." #here passing the message dynamic
** (BugError) I am Bug..

Writing Protocols

Define a Protocol

A Protocol is a way to dispatch to a particular implementation of a function based on the type of the parameter. The macros defprotocol and defimpl are used to define Protocols and Protocol implementations respectively for different types in the following example.

defprotocol Triple do    
  def triple(input)  
end  
​
defimpl Triple, for: Integer do    
  def triple(int) do     
    int * 3   
  end  
end   
​
defimpl Triple, for: List do
  def triple(list) do
    list ++ list ++ list   
  end  
end

Usage

Load the code into iex and execute

iex> Triple.triple(3) 
9
Triple.triple([1, 2])
[1, 2, 1, 2, 1, 2]

Ternary Operator

There is no ternary operator like true ? "yes" : "no" . So, the following is suggested.

"no" = if 1 == 0, do: "yes", else: "no"

Advantage of Kernel.||

When using pipelines, sometimes we break the pipeline for or operation. For example:

result = :input
|> do_something
|> do_another_thing

# Bad
result = (result || :default_output)
|> do_something_else

Indeed, || is only a shortcut for Kernel.|| . We can use Kernel.|| in the pipeline instead to avoid breaking the pipeline.

The code above will be:

result = :input
|> do_something
|> do_another_thing
|> Kernel.||(:default_output)  #<-- This line
|> do_something_else

This above tip is from qhwa​

Checking Out Code Grouping

Code grouping stands for something great. It shows you how your code is grouped when you write multiple lines of code in single line with out using braces. It will be more clear with the following example.

one 1 |> two()

If you want to see how this line of code is grouped into, you can check in the following format..

quote(do: one 1 |> two()) |> Macro.to_string |> IO.puts
one(1 |> two())

So, by using the quote and Macro.to_string you can see how our code was grouped into.

This tip came out in discussion with the creator of Ecto MichalMuskala in the Elixir forum.

Elixir Short Circuit Operators && — ||

These replaces the nested complicated conditions. These are my best friends in the situations dealing with more complex comparisons. Trust me you gonna love this.

The || operator always returns the first expression which is true. Elixir doesn’t care about the remaining expressions, and won’t evaluate them after a match has been found.

||

false || nil || :blackode || :elixir || :jose

Here if you observe the first expression is false next nil is also false in elixir next :blackode which evaluates to true and its value is returned immediately with out evaluating the :elixir and :jose . Similarly if all the statements evaluates to false the last expression is returned.

&&

iex> true && :true && :elixir && 5
5
iex> nil && 100
nil
iex> salary = is_login && is_admin && is_staff && 100_000

This && returns the second expression if the first expression is true or else it returns the first expression with out evaluating the second expression. In the above examples the last one is the situation where we encounter to use the && operator.

Comparing two different data types

I have self experience with this. When I was a novice in elixir, I just compared "5" > 4 unknowingly by an accident and to my surprise it returned with true.

In Elixir every term can compare with every other term. So one has to be careful in comparisons.

iex> x = "I am x "
"I am x "
iex> x > 34
true
iex> x > [1,2,3]
true
iex> [1, 2, 3] < 1234567890
false

Order of Comparison

number < atom < reference < fun < port < pid < tuple < map < list < bitstring (binary)

Arithmetic Operators as Lambda functions

When I see this first time, I said to my self “Elixir is Crazy”. This tip really saves time and it resembles your smartness. In Elixir every operator is a macro. So, we can use them as lambda functions.

iex> Enum.reduce([1,2,3], 0, &+/2)
6
iex> Enum.reduce([1,2,3], 0, &*/2)
0
iex> Enum.reduce([1,2,3], 3, &*/2)
18
iex> Enum.reduce([1,2,3], 3, &-/2)
-1
iex> Enum.reduce([1,2,3], 3, &//2)
0.5

Binary Pattern Matching

This is my recent discovery. I always encounter a situation like converting "$34.56" which is a string and I suppose do arithmetic operations. I usually do something like this before binary pattern matching..

iex> value = "$34.56"
iex ...      |> String.split("$")
iex ...      |> tl
iex ...      |> List.first
iex ...      |> String.to_float
34.56

Tip Approach

This tip makes my day easy. I recently used this is in one of my projects.

iex> "$" <> value = "$34.56"
"$34.56"
iex> String.to_float value  
34.56

Must Know the Differences of Map keys as :atoms and binary(strings)

Before I let you to use this tip, I just want to remind you that :atoms are not garbage collected. Atom keys are great! If you have a defined atoms, you are in no danger. What you should not do is converting user supplied input into atoms without sanitizing them first because it can lead to out of memory. You should also be cautious if you create dynamic atoms in your code.

But, you can use the . to retrieve the data from the keys as map.key unlike the usual notation like map["key"] . That really saves on typing. But, I don’t encourage this because, as programmers we should really care about memory.

iex> map = %{name: "blackode", blog: "medium"}
%{blog: "medium", name: "blackode"}
​
iex> map.name
"blackode"
​
iex> map.blog
"medium"

Be sure that when you try to retrieve a key with . form which is not present in the map, it will raise a key error instead of returning the nil unlike the map["key"] which returns nil if key is not present in a map.

iex> map["age"]
nil

iex> map.age
Bug Bug ..!!** (KeyError) key :age not found in: %{blog: "medium", name: "blackode"}
Bug Bug ..!!

Add Some Color To Your Console Prints

Elixir >=1.4.0 has ANSI color printing option to console. You can have great fun with colors. You can also provide background colors.

iex> import IO.ANSI
iex> IO.puts red <> "red" <> green <> " green" <> yellow <> " yellow" <> reset <> " normal"
iex> IO.puts Enum.join [red, "red", green, " green", yellow, " yellow", reset, " normal"]
red green yellow normal

The red prints in red color, green in green color, yellow in yellow color and normal in white. Have fun with colors…

For more details on color printing check Printex module which I created for fun in Elixir.

Functional Macros as Guard Clauses

We cannot make use of the functions as guard clauses in elixir. It means, when cannot accept custom defined functions. Consider the following lines of code…

defmodule Hello do
  def hello(name, age) when is_kid(age) do
    IO.puts "Hello Kid #{name}"
  end
​
  def hello(name, age) when is_adult(age) do
    IO.puts "Hello Mister #{name}"
  end
​
  def is_kid age do
    age < 12
  end
​
  def is_adult age do
    age > 18
  end
end

Here we defined a module Hello and a function hello that takes two parameters of name and age. So, based on age I am trying IO.putsaccordingly. If you do so you will get an error saying….

** (CompileError) hello.ex:2: cannot invoke local is_kid/1 inside guard
    hello.ex:2: (module)

This is because when cannot accept functions as guards. We need to convert them to macros Lets do that…

defmodule MyGuards do
​
  defmacro is_kid age do
    quote do: unquote(age) < 12
  end
​
  defmacro is_adult age do
    quote do: unquote(age) > 18
  end
​
end
# order of module matters here.....
defmodule Hello do
​
  import MyGuards
​
  def hello(name, age) when is_kid(age) do
    IO.puts "Hello Kid #{name}"
  end
​
  def hello(name, age) when is_adult(age) do
    IO.puts "Hello Mister #{name}"
  end
​
   def hello(name, age) do
    IO.puts "Hello Youth #{name}"
  end
​
end

In the above lines of code, we wrapped all our guards inside a module MyGuards and make sure the module is top of the module Hello so, the macros first gets compiled. Now compile and execute you will see the following output..

iex> Hello.hello "blackode", 21
Hello Mister blackode
:ok
iex> Hello.hello "blackode", 11
Hello Kid blackode
:ok

Starting on Elixir v1.6, you can use defguard/1.

The defguard is also a macro. You can also create private guards with defguardp. Hope, you got the point here. Consider the following example.

NOTE: The defguard and defguardp should reside inside the module like other macros. It raises a compile time error, if some thing that don't fit in the guard clause section when.

Suppose, you want to check the given number is either three or five, you can define the guard as following.

defmodule Number.Guards do
  defguard is_three_or_five(number) when (number===3) or (number===5)
end

Usage

import Number.Guards
defmodule Hello do
  def check_favorite_number(num) when is_three_or_five(num) do
    IO.puts "The given #{num} is on of my favourite numbers"
  end
  def check_favorite_number(_num), do: IO.puts "Not my favorite number"
end

You can also use them inside your code logic as they results boolean value.

iex> import Number.Guards
Number.Guards
​
iex> is_three_or_five(5)
true
​
iex> is_three_or_five(3)
true
​
iex> is_three_or_five(1)
false

Check the following execution screen shot.

Finding whether Module was loaded or not

Sometimes, we have to make sure that certain module is loaded before making a call to the function. We are supposed to ensure the module is loaded.

Code.ensure_loaded? <Module>

iex> Code.ensure_loaded? :kernel
true
iex> Code.ensure_loaded :kernel
{:module, :kernel}

Similarly we are having ensure_compile to check whether the module is compiled or not…

Converting Binary to Capital Atom

Elixir provides a special syntax which is usually used for module names. What is called a module name is an uppercase ASCII letter followed by any number of lowercase or uppercase ASCII letters, numbers, or underscores.

This identifier is equivalent to an atom prefixed by Elixir. So in the defmodule Blackode example Blackode is equivalent to :"Elixir.Blackode"

When we use String.to_atom "Blackode" it converts it into :Blackode But actually we need something like “Blackode” to Blackode. To do that we need to use Module.concat

iex(2)> String.to_atom "Blackode"
:Blackode
iex(3)> Module.concat Elixir,"Blackode"
Blackode

In Command line applications whatever you pass they convert it into binary. So, again you suppose to do some casting operations …

Pattern match [ vs ] destructure.

We all know that = does the pattern match for left and right side. We cannot do [a, b, c] = [1, 2, 3, 4] this raise a MatchError

iex(11)> [a, b, c] = [1, 2, 3, 4]
** (MatchError) no match of right hand side value: [1, 2, 3, 4]

We can use destructure/2 to do the job.

iex(1)> destructure [a, b, c], [1, 2, 3, 4]
[1, 2, 3]
iex(2)> {a, b, c}
{1, 2, 3}

If the left side is having more entries than in right side, it assigns the nil value for remaining entries..

iex> destructure([a, b, c], [1])
iex> {a, b, c} 
{1, nil, nil}

The Goodness of Data decoration [ inspect with :label ] option

We can decorate our output with inspect and label option. The string of label is added at the beginning of the data we are inspecting.

iex(1)> IO.inspect [1, 2, 3], label: "the list "
the list : [1, 2, 3]
[1, 2, 3]

If you closely observe this it again returns the inspected data. So, we can use them as intermediate results in |> pipe operations like following……

[1, 2, 3] 
|> IO.inspect(label: "before change") 
|> Enum.map(&(&1 * 2)) 
|> IO.inspect(label: "after change") 
|> length

You will see the following output

before change: [1, 2, 3]
after change: [2, 4, 6]
3

Piping Anonymous functions

We can pass the anonymous functions in two ways. One is directly using &like following..

[1, 2, 3, 4, 5]
|> length()
|> (&(&1*&1)).()

This is the most weirdest approach. How ever, we can use the reference of the anonymous function by giving its name.

square = & &1 * &1
[1, 2, 3, 4, 5]
|> length()
|> square.()

The above style is much better than previous . You can also use fn to define anonymous functions.

Retrieve Character Integer Codepoints — ?

We can use ? operator to retrieve character integer codepoints.

iex> ?a
97
iex> ?#
35

The following two tips are mostly useful for beginners…

Performing Subtraction on Lists

We can perform the subtraction over lists for removing the elements in list.

iex> [1, 2, 3, 4.5] -- [1, 2]
[3, 4.5]
iex> [1, 2, 3, 4.5, 1] -- [1]  
[2, 3, 4.5, 1]
iex> [1, 2, 3, 4.5, 1] -- [1, 1]
[2, 3, 4.5]
iex> [1, 2, 3, 4.5] -- [6]
[1, 2, 3, 4.5]

We can also perform same operations on char lists too..

iex(12)> 'blackode' -- 'ode'
'black'
iex(13)> 'blackode' -- 'z'    
'blackode'

If the element to subtract is not present in the list then it simply returns the list.

Running Multiple Mix Tasks

mix do deps.get,compile

You can run multiple tasks by separating them with coma ,

How ever you can also create aliases in your mix project in a file called mix.exs .

The project definition looks like the following way when you create one using a mix tool.

def project do
    [app: :project_name,
     version: "0.1.0",
     elixir: "~> 1.4-rc",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     deps: deps()]
  end

You are also allowed to add some extra fields…

Here you have to add the aliases field.

[
 aliases: aliases()
]

Don’t forget to add , at the end when you add this in the middle of list .

The aliases() should return the key-value list.

defp aliases do
  [
    "ecto.setup": ["ecto.create", "ecto.migrate", "ecto.seed"]
  ]
end

So, whenever you run the mix ecto.setup the three tasks ecto.create, ecto.migrate and ecto.seed will run one after the other.

You can also add them directly as following unlike I did with private function.

def project do
    [app: :project_name,
     version: "0.1.0",
     aliases: ["ecto.setup": ["ecto.create", "ecto.migrate", "ecto.seed"]]      
.....
  end

Accessing the Documentation

Elixir stores the documentation inside the bytecode in a memory. You access the documentation with the help of Code.get_docs/2 function . This means, the documentation accessed when it is required, but not when it is loaded in the virtual machine like iex

Suppose you defined a module in memory like ones you defined in IEx, cannot have their documentation accessed as they do not have their bytecode written to disk.

Let us check this…

Create a module with name test.ex with the following code. You can copy and paste it.

defmodule Test do
  @moduledoc """
  This is the test module docs
  """
​
  @doc """
  This is the documentation of hello function
  """
  def hello do
    IO.puts "hello"
  end
end

Now stay in the directory where your file exists and run the command

$ iex test.ex

Now you can access the function definitions but not the documentation.

iex> Test.hello
hello
:ok

That means the code is compiled but documentation is not stored in the memory. So, you cannot access the docs. Lets check that…

iex> Code.get_docs Hello, :moduledoc
nil

You will see the output as nil when you are trying to access the docs of the module you have created so far. This is because, the bytecode is not available in disk. In simple way beam file is not present. Lets do that...

Press Ctrl+C twice so you will come out of the shell and this time you run the command as

$ elixirc test.ex

After running the command, you will see a file with name Elixir.Test.beam . Now the bytecode for the module Test is available in memory. Now you can access the documentation as follows...

$ iex
iex> Code.get_docs Test, :moduledoc
{3, "This is the test module docs\n"}

The output is tuple with two elements. The first element is the line number of the documentation it starts and second element is the actual documentation in the binary form.

You can read more about this function here​

Dynamic Function Name in Elixir Macro

The hack is name of a function should be an atom instead of binary.

defmacro gen_function(fun_name) do
  quote do 
    def unquote(:"#{fun_name}")() do
      # your code...
    end
  end
end

Printing List as List without ASCII-Encoding

You know that when the list contains all the numbers as ASCII values, it will list out those values instead of the original numbers. Lets check that…

iex> IO.inspect [97, 98]
'ab'
'ab'

The code point of a is 97 and b is 98 hence it is listing out them as char_list. However you can tell the IO.inspect to list them as list itself with option char_lists: :as_list .

iex> IO.inspect [97, 98], charlists: :as_lists
[97, 98]
'ab'

Open iex and type h Inspect.Opts, you will see that Elixir does this kind of thing with other values as well, specifically structs and binaries.

Fetching out file name and line number the expression is on

defmacro __ENV__()

This macro gives the current environment information. You can get the information like current filename line function and others…

iex(4)> __ENV__.file
"iex"
​
iex(5)> __ENV__.line
5

Creating Manual Pids for Unit Testing

You can create the pid manually in Elixir with pid function. This comes with two flavors.

def pid(string)

Creates the pid from the string.

iex> pid("0.21.32")
#PID<0.21.32>

def pid(a, b, c)

Creates a PID with 3 non negative integers passed as arguments to the function.

iex> pid(0, 21, 32)
#PID<0.21.32>

Why do you create the pids manually?

Suppose, you are writing a library and you want to test one of your functions for the type pid, then you can create one and test with it.

You cannot create the pid like assigning pid = #PID<0.21.32> because # is considered as comment here.

iex(6)> pid = #PID<0.21.32>
...(6)>

When you do like above, iex shell just wait for more input as #PID<0.21.32> is treated as comment.

Now you enter another data to complete the expression. The entered value is the value of the pid. Lets check that…

iex(6)> pid = #PID<0.21.32>      # here expression is not complete
...(6)> 23    # here we are giving the value 23
23            # expression is complete
iex(7)> pid
23

Replacing the String with global option

The String.replace function will replace the given the pattern with replacing pattern. By default, it replaces all the occurrences of the pattern. Lets check that…

iex(1)> str = "[email protected], [email protected]"    
"[email protected], [email protected]"
​
iex(2)> String.replace str,"@","#"
"hello#hi.com, blackode#medium.com

The String.replace str, "@", "#"is same as String.replace str, "@", "#", global: true

But, if you want to replace only the first occurrence of the pattern, you need to pass the option global: false . So, it replaces only the first occurrence of @ . Lets check that…

iex(3)> String.replace str, "@", "#", global: false
"hello#hi.com, [email protected]"

Here only first @ is replaced with #.

Memory Usage

You can check the memory usage (in bytes) with :erlang.memory

iex(1)> :erlang.memory
[total: 16221568, processes: 4366128, processes_used: 4364992, system: 11855440,
 atom: 264529, atom_used: 250685, binary: 151192, code: 5845369, ets: 331768]

However, you can pass option like :erlang.memory :atom to get the memory usage of atoms.

iex(2)> :erlang.memory :atom
264529

Picking out the elements in List

We all know that a proper list is a combination of head and tail like [head | tail] . We can use the same principle for picking out the elements in the list like the following way…

iex> [first, second, third, fourth | _rest] = [1, 2, 3, 4, 5, 6, 7]
[1, 2, 3, 4, 5, 6, 7]
iex> first
1
iex> {second, third, fourth}
{2, 3, 4}

The combination effect of get_in /Access.all()

We all know that the get_in function is used to extract the key which is deeper inside the map by providing the list with keys like a following way…

iex> user = %{"name" => {"first_name" => "blackode", "last_name" => "john" }}
%{"name" => %{"first_name" => "blackode", "last_name" => "john"}}
iex > get_in user, ["name", "first_name"]
"blackode"

But, if there is a list of maps [maps] where you have to extract first_name of the each map, generally we go for enum . We can also achieve this by using the get_in and Access.all()

iex> users=[%{"user" => %{"first_name" => "john", "age" => 23}},
            %{"user" => %{"first_name" => "hari", "age" => 22}},
            %{"user" => %{"first_name" => "mahesh", "age" => 21}}]
# that is a list of maps 
iex> get_in users, [Access.all(), "user", "age"]
[23, 22, 21]
​
iex> get_in users, [Access.all(), "user", "first_name"]
["john", "hari", "mahesh"]