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Killer Elixir-Tips
Killer Elixir-Tips
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...
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 HERE1
# IEx.configure colors: [enabled: true]
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# IEx.configure colors: [ eval_result: [ :cyan, :bright ] ]
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IO.puts IO.ANSI.red_background() <> IO.ANSI.white() <> " ❄❄❄ Good Luck with Elixir ❄❄❄ " <> IO.ANSI.reset
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Application.put_env(:elixir, :ansi_enabled, true)
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IEx.configure(
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colors: [
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eval_result: [:green, :bright] ,
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eval_error: [[:red,:bright,"Bug Bug ..!!"]],
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eval_info: [:yellow, :bright ],
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],
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default_prompt: [
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"\e[G", # ANSI CHA, move cursor to column 1
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:white,
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"I",
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:red,
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"❤" , # plain string
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:green,
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"%prefix",:white,"|",
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:blue,
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"%counter",
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:white,
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"|",
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:red,
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"▶" , # plain string
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:white,
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"▶▶" , # plain string
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# ❤ ❤-»" , # plain string
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:reset
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] |> IO.ANSI.format |> IO.chardata_to_string
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)
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Creating Custom Sigils and Documenting
Each
x sigil calls its respective sigil_x definitionDefining Custom Sigils
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defmodule MySigils do
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#returns the downcasing string if option l is given then returns the list of downcase letters
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def sigil_l(string,[]), do: String.downcase(string)
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def sigil_l(string,[?l]), do: String.downcase(string) |> String.graphemes
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#returns the upcasing string if option l is given then returns the list of downcase letters
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def sigil_u(string,[]), do: String.upcase(string)
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def sigil_u(string,[?l]), do: String.upcase(string) |> String.graphemes
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end
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usage
Load the module into iex
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iex> import MySigils
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iex> ~l/HELLO/
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"hello"
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iex> ~l/HELLO/l
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["h", "e", "l", "l", "o"]
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iex> ~u/hello/
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"HELLO"
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iex> ~u/hello/l
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["H", "E", "L", "L", "O"]
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Custom Error Definitions
Define Custom Error
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defmodule BugError do
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defexception message: "BUG BUG .." # message is the default
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end
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Usage
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iex bug_error.ex
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iex> raise BugError
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** (BugError) BUG BUG ..
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iex> raise BugError, message: "I am Bug.." #here passing the message dynamic
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** (BugError) I am Bug..
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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.1
defprotocol Triple do
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def triple(input)
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end
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defimpl Triple, for: Integer do
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def triple(int) do
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int * 3
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end
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end
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defimpl Triple, for: List do
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def triple(list) do
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list ++ list ++ list
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end
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end
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Usage
Load the code into
iex and execute1
iex> Triple.triple(3)
2
9
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Triple.triple([1, 2])
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[1, 2, 1, 2, 1, 2]
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Ternary Operator
There is no ternary operator like
true ? "yes" : "no" . So, the following is suggested.1
"no" = if 1 == 0, do: "yes", else: "no"
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Advantage of Kernel.||
When using pipelines, sometimes we break the pipeline for
or operation. For example:1
result = :input
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|> do_something
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|> do_another_thing
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1
# Bad
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result = (result || :default_output)
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|> do_something_else
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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:
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result = :input
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|> do_something
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|> do_another_thing
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|> Kernel.||(:default_output) #<-- This line
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|> do_something_else
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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.
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one 1 |> two()
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If you want to see how this line of code is grouped into, you can check in the following format..
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quote(do: one 1 |> two()) |> Macro.to_string |> IO.puts
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one(1 |> two())
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So, by using the
quote and Macro.to_string you can see how our code was grouped into.
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.||
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false || nil || :blackode || :elixir || :jose
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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.&&
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iex> true && :true && :elixir && 5
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5
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iex> nil && 100
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nil
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iex> salary = is_login && is_admin && is_staff && 100_000
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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.
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iex> x = "I am x "
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"I am x "
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iex> x > 34
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true
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iex> x > [1,2,3]
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true
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iex> [1, 2, 3] < 1234567890
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false
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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.
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iex> Enum.reduce([1,2,3], 0, &+/2)
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6
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iex> Enum.reduce([1,2,3], 0, &*/2)
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0
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iex> Enum.reduce([1,2,3], 3, &*/2)
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18
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iex> Enum.reduce([1,2,3], 3, &-/2)
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-1
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iex> Enum.reduce([1,2,3], 3, &//2)
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0.5
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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..Could not load image
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iex> value = "$34.56"
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iex ... |> String.split("quot;)
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iex ... |> tl
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iex ... |> List.first
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iex ... |> String.to_float
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34.56
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Tip Approach
This tip makes my day easy. I recently used this is in one of my projects.
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iex> "quot; <> value = "$34.56"
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"$34.56"
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iex> String.to_float value
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34.56
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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.Could not load image
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iex> map = %{name: "blackode", blog: "medium"}
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%{blog: "medium", name: "blackode"}
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iex> map.name
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"blackode"
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iex> map.blog
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"medium"
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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.1
iex> map["age"]
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nil
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iex> map.age
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Bug Bug ..!!** (KeyError) key :age not found in: %{blog: "medium", name: "blackode"}
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Bug Bug ..!!
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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.1
iex> import IO.ANSI
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iex> IO.puts red <> "red" <> green <> " green" <> yellow <> " yellow" <> reset <> " normal"
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iex> IO.puts Enum.join [red, "red", green, " green", yellow, " yellow", reset, " normal"]
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red green yellow normal
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The red prints in red color, green in green color, yellow in yellow color and normal in white. Have fun with colors…
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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…1
defmodule Hello do
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def hello(name, age) when is_kid(age) do
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IO.puts "Hello Kid #{name}"
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end
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def hello(name, age) when is_adult(age) do
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IO.puts "Hello Mister #{name}"
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end
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def is_kid age do
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age < 12
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end
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def is_adult age do
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age > 18
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end
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end
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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….1
** (CompileError) hello.ex:2: cannot invoke local is_kid/1 inside guard
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hello.ex:2: (module)
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This is because when cannot accept functions as guards. We need to convert them to
macros Lets do that…1
defmodule MyGuards do
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defmacro is_kid age do
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quote do: unquote(age) < 12
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end
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defmacro is_adult age do
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quote do: unquote(age) > 18
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end
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end
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# order of module matters here.....
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defmodule Hello do
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import MyGuards
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def hello(name, age) when is_kid(age) do
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IO.puts "Hello Kid #{name}"
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end
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def hello(name, age) when is_adult(age) do
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IO.puts "Hello Mister #{name}"
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end
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def hello(name, age) do
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IO.puts "Hello Youth #{name}"
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end
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end
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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..1
iex> Hello.hello "blackode", 21
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Hello Mister blackode
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:ok
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iex> Hello.hello "blackode", 11
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Hello Kid blackode
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:ok
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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.1
defmodule Number.Guards do
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defguard is_three_or_five(number) when (number===3) or (number===5)
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end
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Usage
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import Number.Guards
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defmodule Hello do
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def check_favorite_number(num) when is_three_or_five(num) do
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IO.puts "The given #{num} is on of my favourite numbers"
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end
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def check_favorite_number(_num), do: IO.puts "Not my favorite number"
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end
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You can also use them inside your code logic as they results
boolean value.1
iex> import Number.Guards
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Number.Guards
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iex> is_three_or_five(5)
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true
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iex> is_three_or_five(3)
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true
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iex> is_three_or_five(1)
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false
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Check the following execution screen shot.
ScreenShot Defguard Execution
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.
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Code.ensure_loaded? <Module>
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iex> Code.ensure_loaded? :kernel
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true
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iex> Code.ensure_loaded :kernel
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{:module, :kernel}
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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.concat1
iex(2)> String.to_atom "Blackode"
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:Blackode
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iex(3)> Module.concat Elixir,"Blackode"
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Blackode
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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 MatchError1
iex(11)> [a, b, c] = [1, 2, 3, 4]
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** (MatchError) no match of right hand side value: [1, 2, 3, 4]
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We can use
destructure/2 to do the job.1
iex(1)> destructure [a, b, c], [1, 2, 3, 4]
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[1, 2, 3]
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iex(2)> {a, b, c}
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{1, 2, 3}
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If the left side is having more entries than in right side, it assigns the
nil value for remaining entries..1
iex> destructure([a, b, c], [1])
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iex> {a, b, c}
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{1, nil, nil}
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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.1
iex(1)> IO.inspect [1, 2, 3], label: "the list "
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the list : [1, 2, 3]
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[1, 2, 3]
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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
[1, 2, 3]
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|> IO.inspect(label: "before change")
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|> Enum.map(&(&1 * 2))
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|> IO.inspect(label: "after change")
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|> length
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You will see the following
output1
before change: [1, 2, 3]
2
after change: [2, 4, 6]
3
3
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Piping Anonymous functions
We can pass the anonymous functions in two ways. One is directly using
&like following..1
[1, 2, 3, 4, 5]
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|> length()
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|> (&(&1*&1)).()
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This is the most weirdest approach. How ever, we can use the reference of the anonymous function by giving its name.
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square = & &1 * &1
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[1, 2, 3, 4, 5]
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|> length()
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|> square.()
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The above style is much better than previous . You can also use
fn to define anonymous functions.Or use
Kernel.then/2 function since 1.12.01
[1, 2, 3, 4, 5]
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|> length()
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|> then(& &1 * &1)
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Retrieve Character Integer Codepoints — ?
We can use
? operator to retrieve character integer codepoints.1
iex> ?a
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97
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iex> ?#
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35
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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.
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iex> [1, 2, 3, 4.5] -- [1, 2]
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[3, 4.5]
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iex> [1, 2, 3, 4.5, 1] -- [1]
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[2, 3, 4.5, 1]
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iex> [1, 2, 3, 4.5, 1] -- [1, 1]
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[2, 3, 4.5]
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iex> [1, 2, 3, 4.5] -- [6]
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[1, 2, 3, 4.5]
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We can also perform same operations on char lists too..
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iex(12)> 'blackode' -- 'ode'
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'black'
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iex(13)> 'blackode' -- 'z'
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'blackode'
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If the element to subtract is not present in the list then it simply returns the list.
Running Multiple Mix Tasks
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mix do deps.get,compile
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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.1
def project do
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[app: :project_name,
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version: "0.1.0",
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elixir: "~> 1.4-rc",
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build_embedded: Mix.env == :prod,
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start_permanent: Mix.env == :prod,
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deps: deps()]
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end
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You are also allowed to add some extra fields…
Here you have to add the
aliases field.1
[
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aliases: aliases()
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]
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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.1
defp aliases do
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[
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"ecto.setup": ["ecto.create", "ecto.migrate", "ecto.seed"]
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]
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end
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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.
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def project do
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[app: :project_name,
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version: "0.1.0",
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aliases: ["ecto.setup": ["ecto.create", "ecto.migrate", "ecto.seed"]]
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.....
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end
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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 iexSuppose 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.1
defmodule Test do
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@moduledoc """
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This is the test module docs
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"""
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@doc """
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This is the documentation of hello function
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"""
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def hello do
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IO.puts "hello"
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end
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end
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Now stay in the directory where your file exists and run the command
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$ iex test.ex
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Now you can access the function definitions but not the documentation.
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iex> Test.hello
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hello
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:ok
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That means the code is compiled but documentation is not stored in the memory. So, you cannot access the docs. Lets check that…
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iex> Code.get_docs Hello, :moduledoc
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nil
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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 as1
$ elixirc test.ex
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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...1
$ iex
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iex> Code.get_docs Test, :moduledoc
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{3, "This is the test module docs\n"}
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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.
Dynamic Function Name in Elixir Macro
The hack is name of a function should be an atom instead of binary.
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defmacro gen_function(fun_name) do
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quote do
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def unquote(:"#{fun_name}")() do
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# your code...
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end
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end
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end
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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…
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iex> IO.inspect [97, 98]
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'ab'
3
'ab'
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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 .1
iex> IO.inspect [97, 98], charlists: :as_lists
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[97, 98]
3
'ab'
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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
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defmacro __ENV__()
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This macro gives the current environment information. You can get the information like current
filename line function and others…1
iex(4)> __ENV__.file
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"iex"
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4
iex(5)> __ENV__.line
5
5
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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.
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iex> pid("0.21.32")
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#PID<0.21.32>
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def pid(a, b, c)
Creates a PID with 3 non negative integers passed as arguments to the function.
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iex> pid(0, 21, 32)
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#PID<0.21.32>
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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.1
iex(6)> pid = #PID<0.21.32>
2
...(6)>
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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…
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iex(6)> pid = #PID<0.21.32> # here expression is not complete
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...(6)> 23 # here we are giving the value 23
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23 # expression is complete
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iex(7)> pid
5
23
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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…1
iex(1)> str = "[email protected], [email protected]"
3
4
iex(2)> String.replace str,"@","#"
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"hello#hi.com, blackode#medium.com
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The
String.replace str, "@", "#"is same as String.replace str, "@", "#", global: trueBut, 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…1
iex(3)> String.replace str, "@", "#", global: false
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"hello#hi.com, [email protected]"
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Here only first
@ is replaced with #.
Memory Usage
You can check the memory usage (in bytes) with
:erlang.memory1
iex(1)> :erlang.memory
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[total: 16221568, processes: 4366128, processes_used: 4364992, system: 11855440,
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atom: 264529, atom_used: 250685, binary: 151192, code: 5845369, ets: 331768]
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However, you can pass option like
:erlang.memory :atom to get the memory usage of atoms.1
iex(2)> :erlang.memory :atom
2
264529
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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…1
iex> [first, second, third, fourth | _rest] = [1, 2, 3, 4, 5, 6, 7]
2
[1, 2, 3, 4, 5, 6, 7]
3
iex> first
4
1
5
iex> {second, third, fourth}
6
{2, 3, 4}
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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…
1
iex> user = %{"name" => {"first_name" => "blackode", "last_name" => "john" }}
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%{"name" => %{"first_name" => "blackode", "last_name" => "john"}}
3
iex > get_in user, ["name", "first_name"]
4
"blackode"
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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()1
iex> users=[%{"user" => %{"first_name" => "john", "age" => 23}},
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%{"user" => %{"first_name" => "hari", "age" => 22}},
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%{"user" => %{"first_name" => "mahesh", "age" => 21}}]
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# that is a list of maps
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iex> get_in users, [Access.all(), "user", "age"]
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[23, 22, 21]
7
8
iex> get_in users, [Access.all(), "user", "first_name"]
9
["john", "hari", "mahesh"]
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Note: If the key is not present in map, then it returns nil Warning: When you use the
get_in along with Access.all() , as the first value in the list of keys like above, the users datatype should be list. If you pass the map, it returns the error.1
iex(17)> list = [%{name: "john"}, %{name: "mary"}, %{age: 34}]
2
[%{name: "john"}, %{name: "mary"}, %{age: 34}]
3
iex(18)> get_in(list, [Access.all(), :name])
4
["john", "mary", nil]
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In the above lines of code returns the
nil for key which is not in the map.1
iex(19)> get_in(%{name: "blackode"}, [Access.all(), :name])
2
** (RuntimeError) Access.all/0 expected a list, got: %{name: "blackode"}
3
(elixir) lib/access.ex:567: Access.all/3
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In the above lines of code returns the error for passing map .
However, you can change the position of the Access.all() in the list. But the before key should return the list. Check the following lines of code.
Deep Dive
We can also use the Access.all() with functions like update_in, get_and_update_in, etc..
For instance, given a user with a list of books, here is how to deeply traverse the map and convert all book names to uppercase:
1
iex> user = %{name: "john", books: [%{name: "my soul", type: "tragedy"}, %{name: "my heart", type: "romantic"}, %{name: "my enemy", type: "horror"}]}
2
iex> update_in user, [:books, Access.all(), :name], &String.upcase/1
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%{books: [%{name: "MY SOUL", type: "tragedy"}, %{name: "MY HEART", type: "romantic"}, %{name: "MY ENEMY", type: "horror"}], name: "john"}
4
iex> get_in user, [:books, Access.all(), :name]
5
["my soul", "my heart", "my enemy"]
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Here, user is not a list unlike in the previous examples where we passed the users as a list. But, we changed the position of
Access.all() and inside the list of keys [:books, Access.all(), :name], the value of the key :books should return the list, other wise it raises an error.
Data Comprehension along with filters using FOR
We achieve the data comprehension through
for x <- [1, 2, 3], do: x + 1 . But we can also add the comprehension along with filter.