Variable In Ruby on Rails: A Comprehensive Guide With Examples

Variable In Ruby on Rails

In the world of programming, variables play a crucial role in storing and manipulating data, as it’s also important to know variable in ruby on rails.

In the Ruby on Rails framework, variables are an essential concept that every developer must understand.

This comprehensive guide aims to provide you with a solid understanding of variable in Ruby on Rails, covering their definition, types, scope, and best practices for usage.

What Is Ruby on Rails?

Technically speaking, a well-known Ruby on Rails is a Rails backend framework for creating web applications built in the Ruby programming language. 

The RoR was created by David Heinemeier Hansson under the MIT License.

RoR is compatible with the model-view-controller (MVC) architecture, which provides basic database structure, web pages, and web services. 

RoR employs web standards like JSON or XML to transport data and HTML, CSS, and JavaScript to create user interfaces.

Ruby on Rails operates under two guiding concepts, including:

1. DRY (Don’t Repeat Yourself)

Ruby on Rails adheres to the DRY philosophy of software development to avoid repetition of data and codes.

2. The CoC (Convention Over Configuration)

It offers a variety of suggestions for how to carry out various tasks in a building web application.

The latest version Ruby on Rails 7, a 17-year-old app web development framework, is also readily available today. 

What Is Variable In Ruby on Rails?

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Variables are placeholders used to store and refer to values in a program. 

They provide a means of accessing and manipulating data at different stages of execution. 

In Ruby on Rails, variables are dynamically typed, meaning they can hold values of any type and can change their type during runtime.

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Variable Types in Ruby on Rails 

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In Ruby on Rails, variables can be categorized into several types:

1. Instance Variables

2. Class Variables

3. Local Variables

4. Global Variables

5. Constant Variables

Let’s understand all the variable types in detail.

1. Instance Variables

Instance variables are denoted by the ‘@’ symbol followed by the variable name. 

They are used to store data that is unique to each instance of a class.

They can be accessed and modified by different methods within the instance. 

Example 1:

#!/usr/bin/ruby

class Customer

   def initialize(id, name, addr)

      @cust_id = id

      @cust_name = name

      @cust_addr = addr

   end

   def display_details()

      puts “Customer id #@cust_id

      puts “Customer name #@cust_name

      puts “Customer address #@cust_addr

   end

end

# Create Objects

cust1 = Customer.new(“1”, “Jiya”, “Sky Apartments, Delhi”)

cust2 = Customer.new(“2”, “Peter”, “New RajivGandhi road, Punjab”)

# Call Methods

cust1.display_details()

cust2.display_details()

In this case, instance variables @cust_id, @cust_name, and @cust_addr are used. The followed outcome is:

Customer id 1

Customer name Jiya

Customer address Sky Apartments, Delhi

Customer id 2

Customer name Peter

Customer address New RajivGandhi road, Punjab

Example 2:

#!/usr/bin/ruby   

class States   

   def initialize(name)   

      @states_name=name   

   end   

   def display()   

      puts “States name #@states_name”   

    end   

end   

# Create Objects   

first=States.new(“Kerala”)   

second=States.new(“Gujarat”)   

third=States.new(“Rajasthan”)   

fourth=States.new(“Tripura”)   

# Call Methods   

first.display()   

second.display()   

third.display()   

fourth.display()  

The instance variable in the example above is @states_name. The followed outcome is:

States name Kerala

States name Gujarat 

States name Rajasthan  

States name Tripura

2. Class Variables

Class variables are denoted by ‘@@’ followed by the variable name. 

They are shared among all instances of a class and are commonly used to store data that is common to all instances. However, changes to class variables will affect all instances.

Example 1: 

#!/usr/bin/ruby

class Customer

   @@no_of_customers = 0

   def initialize(id, name, addr)

      @cust_id = id

      @cust_name = name

      @cust_addr = addr

   end

   def display_details()

      puts “Customer id #@cust_id”

      puts “Customer name #@cust_name”

      puts “Customer address #@cust_addr”

   end

   def total_no_of_customers()

      @@no_of_customers += 1

      puts “Total number of customers: #@@no_of_customers

   end

end

# Create Objects

cust1 = Customer.new(“1”, “Jiya”, “Sky Apartments, Delhi”)

cust2 = Customer.new(“2”, “Peter”, “New RajivGandhi road, Punjab”)

# Call Methods

cust1.total_no_of_customers()

cust2.total_no_of_customers()

Here, the class variable @@no_of_customers is used. The followed outcome is:

Total number of customers: 1

Total number of customers: 2

Example 2: 

#!/usr/bin/ruby   

class States   

   @@no_of_states=0   

   def initialize(name)   

      @states_name=name   

      @@no_of_states += 1   

   end   

   def display()   

     puts “State name #@state_name”   

    end   

    def total_no_of_states()   

       puts “Total number of states written: #@@no_of_states”   

    end   

end   

# Create Objects   

first=States.new(“Kerala”)   

second=States.new(“Gujarat”)   

third=States.new(“Rajasthan”)   

fourth=States.new(“Tripura”)   

# Call Methods   

first.total_no_of_states()   

second.total_no_of_states()   

third.total_no_of_states()   

fourth.total_no_of_states()

Here, the class variable @@no_of_states is used. The followed outcome is:

Total number of states written: 4

Total number of states written: 4

Total number of states written: 4

Total number of states written: 4

3. Local Variables

Local variables are declared without any prefix and are used within a specific scope, such as a method or block. They are not accessible outside of their defined scope.

An underscore (_) or a lowercase letter (a-z) must always come first in the name of a local variable. These variables are exclusive to the section of code where they were created. 

A local variable can only be accessed from the block in which it was initialized. External to the method, local variables are not accessible. The local variables do not require initialization.

Example 1:

age = 10

_Age = 20

Example 2:

color = “green”

_person = “Shannon”

4. Global Variables

Global variables are denoted by the ‘$’ symbol followed by the variable name. 

They can be accessed from anywhere within the application, making them accessible across different scopes.

Global variables should be used sparingly as they can introduce complexity and potential issues in large applications. 

It is recommended to limit their usage to cases where they provide a significant benefit.

Example 1:

#!/usr/bin/ruby

$global_variable = 10

class Class1

   def print_global

      puts “Global variable in Class1 is #$global_variable

   end

end

class Class2

   def print_global

      puts “Global variable in Class2 is #$global_variable

   end

end

class1obj = Class1.new

class1obj.print_global

class2obj = Class2.new

class2obj.print_global

A global variable is used here, $global_variable. The followed outcome is:

Global variable in Class1 is 10

Global variable in Class2 is 10

Example 2:

#!/usr/bin/ruby   

$global_var = “GLOBAL”   

class One   

  def display   

     puts “Global variable in One is #$global_var”   

  end   

end   

class Two   

  def display   

     puts “Global variable in Two is #$global_var”   

  end   

end   

oneobj = One.new   

oneobj.display   

twoobj = Two.new   

twoobj.display  

In the above example, $global_var is the global variable. The followed outcome is:

Global variable in One is GLOBAL

Global variable in Two is GLOBAL

5. Constant Variables

Constant variables are declared using uppercase letters and are used to store values that remain unchanged throughout the program’s execution. 

They provide a way to define and access constants across classes and modules.

Example 1:

#!/usr/bin/ruby

class Example

   VAR1 = 100

   VAR2 = 200

   def show

      puts “Value of first Constant is #{VAR1}”

      puts “Value of second Constant is #{VAR2}”

   end

end

# Create Objects

object = Example.new()

object.show

VAR1 and VAR2 in this case are constants. The followed outcome is:

Value of first Constant is 100

Value of second Constant is 200

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Now, we are going to understand variable scope in Ruby on Rails.

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Variable Scope 

The scope of a variable determines its accessibility and lifespan within a program. Ruby on Rails follows a set of rules for variable scoping:

  • Local variables are only accessible within the block, method, or module where they are defined.
  • Instance variables are accessible within the instance of a class and any methods within that instance.
  • Class variables are accessible across different instances of a class.
  • Global variables are accessible from anywhere within the application.
  • Constant variables are accessible across classes and modules.

Let’s understand the naming conventions and some of the best practices for the variable in ruby on rails.

Naming Conventions and Best Practices

To ensure clarity and maintainability of your code, it is important to follow naming conventions and best practices when working with variables in Ruby on Rails:

  • Utilize meaningful and descriptive names that explain the aim of the variable.
  • Avoid using single-letter variable names unless they have a clear meaning.
  • Follow the snake_case naming convention for local and instance variables.
  • Use PascalCase for class variables.
  • Use uppercase for constant variables.
  • Avoid using reserved keywords as variable names.

Ruby is a language that is case sensitive. age and Age are two separate variable names, according to this. Case matters in most languages. 

For Example:

#!/usr/bin/ruby

i = 5

p i

I = 7

p I

Two variables, I and i, are defined in the code sample. They have various values.

Alphanumeric characters and the underscore _ character can be used to name variables in Ruby. A variable cannot have a numeric prefix. 

This helps the interpreter distinguish between a literal number and a variable. Capital letters are not permitted to start variable names. 

In Ruby, an identifier is regarded as a constant if it starts with a capital letter.

Let’s say,

#!/usr/bin/ruby

name = “Jena”

placeOfBirth = “Barcelona”

placeOfBirth = “NewYork”

favorite_season = “spring”

n1 = 2

n2 = 4

n3 = 7

p name, placeOfBirth, favorite_season

p n1, n2, n3

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Variable Initialization 

Variables in Ruby on Rails can be initialized at the point of declaration or later in the code. 

It is good practice to initialize variables with default values to avoid unexpected behavior.

# Example of variable initialization

name = “Harry”

age = 35

Variable Interpolation 

Variable interpolation allows you to embed variables within strings to create dynamic content. 

In Ruby on Rails, this is achieved by using the ‘#{}’ syntax.

name = “Harry”

puts “Hello, #{name}!”

In a Ruby string, variables can be used in the following ways:

  1. Using String Interpolation
  2. Using Format Specifiers
  3. Using Named Arguments
  4. Using String Concatenation

Let’s understand all with ruby example;

1. Using String Interpolation

With the following way, string interpolation (or variable substitution) can use:

name = “Peter”

age = 17

puts “#{name} is #{age} years old!”

# output: “Peter is 17 years old”

The resultant string expands the variables (given in #{ }) into the corresponding values.

2. Using Format Specifiers

Using “format specifiers”—field type characters preceded with %, which describe how their associated substitution arguments should be interpreted—you can format a string similarly to how sprintf does. 

The %s format specification, for instance, can be used to specify that the following string interpretation should be applied to its corresponding argument:

color = “Red”

puts “I love %s color!” % color

# output: “I love Red color!”

In a string, you are free to use as many format specifiers as you like. However, the parameters should be given as an Array holding the values to be substituted when the format specification calls for more than one substitution. For instance:

name = “Peter”

age = 17

puts “%s is %d years old” % [name, age]

# output: “Peter is 17 years old”

The two format specifiers (%s for string and %d for decimal number) are replaced with their respective parameters as provided in the array after the % sign, as you can see from the example above.

3. Using Named Arguments

In a Hash, you can specify named arguments from the text together with the substitution arguments they require as follows:

name = “Peter”

age = 17

puts “%{a} is %{b} years old” % {a: name, b: age}

# output: “Peter is 17 years old”

4. Using String Concatenation

You can insert the + operator to join string parts and variables together. For example:

color = “Red”

puts “I love ” + color + ” color!” 

# output: “I love Red color!”

Some Other Aspects of Ruby Variables

1. Null Variables

In Ruby on Rails, there is no specific null value like in some other programming languages. Instead, the value ‘nil’ is used to represent the absence of a value.

2. Dynamic Variables 

Dynamic variables are variables whose names are determined during runtime. They provide flexibility in handling varying data structures.

3. Thread-local Variables

Those variables who are specific to each thread are known as Thread-local variables. They allow for thread-safe storage and retrieval of data.

4. Variable Shadowing 

Variable shadowing occurs when a variable declared within an inner scope has the same name as a variable in an outer scope. In cases like this, the inner variable comes before, “shadowing” the outer variable.

Conclusion

In conclusion, variables are a fundamental aspect of programming in Ruby on Rails. 

They allow developers to store, manipulate, and access data efficiently. 

Understanding the different types of variables and their scopes is crucial for writing clean and maintainable code. 

By following the best practices outlined in this guide, you can improve the readability and reliability of your Ruby on Rails applications.

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