What is the practical purpose of instance variables?

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I'm new to ruby rails, and I'm struggling to understand what the purpose of instance variables are.

What is the point of making a variable into an instance variable?

Basically why would I do this:

class User
   def initialize(var1)
     @name = var1
   end
end

over this:

class User
   def initialize(var1)
     name = var1
   end
end

And in what types of situations would I want to use an instance variable over just a regular variable?


The practical use for this is that if you need a variable to persist across function calls, make it an instance variable.

after you define the instance variable, you can call the value of this on another function and you will have the value.

In general an instance variable is local and persisted inside an instance of an object, whereas a local variable is only local and persisted inside a function/object/block scope.

in your example if you have another method on your user class, you can use the value of @name on that other method, but coulnd't use var1 outside of initialize method.

class User
   def initialize(var1)
     @name = var1
   end

   def greetings
     "hello #{@name}"
   end    
end

What is the practical purpose of instance variables?, The instance variables shared by two methods are an important source of Use a default of private on instance class variables unless you know that this class it is the same basic programming technique: it is a current practice to redefine a  Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed. Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object's state that must be present throughout the class.


class People
  def age
    @age
  end

  def age= age
    @age = age
  end
end

def show people
  age = people.age || '22'
  p "Hello, my age is #{age}"
end

people = People.new
show people
=> 'Hello, my age is 22'
age
=> NameError: undefined local variable or method 'age' for main:Object
user.age = 21
greet people
=> 'Hello, my age is 21'
@age
=> nil

Notice that both variable types are local to a specific context though. @age is defined within the people instance, so when you call people.age you are calling the age function in the age instance, in which @age is defined. age is only defined in the show function, so when you call p "Hello, my age is #{age}" you are able to get a value for age because you are within the scope in which it is defined.

Instance Variable, This article on "instance variable in java" will give you an introduction to Java instances along with a practical demonstration. An instance variable is a part of the object that contains it and cannot live independently of it. All object instances have their own copies of instance variables. One object instance can change values of its instance variables without affecting all other instances. Instance variables can be used by all methods of a class unless the methods are marked with "static" modifier.


Because your instance variable will be accessible to your view code, including within forms and passing data to paths. That's probably the most common, practical use case for them. In your example, I could do the following:

<p>User: <%= "#{@name}" %></p>

And, instead of seeing "@name" in my corresponding paragraph in the rendered H.T.M.L, you'd see the value of that instance variable - whereas the inverse:

<p>User: <%= "#{name}" %></p>

...will probably result in an ActionView error, since "name" is undefined, according to it.

Instance Variable In Java, How to Define & Use Ruby Instance Variables. You define Don't forget to practice now, play with the code examples & come up with your own. Thanks for  Instance variables are available to any method bound to an object instance. As a practical matter, this generally gives it scope within some instantiated class object. When an object is allocated in the heap, there is a slot in it for each instance variable value. Therefore an instance variable is created when an object is created and destroyed when the object is destroyed.


Read This If You Want to Understand Instance Variables in Ruby, Instance variable in Java are used by Objects to store their states. Instance variables can use any of the four access levels; They can be  Expert Answer. 1- Purpose of an instance variable :- A class provides an instance variable (or several instance variables) when each object of the class must maintain information separately from all other objects of view the full answer.


Instance variable in java with example, You just refer to them slightly differently. Getting Values. To get to the value of an instance variable, you use dot notation, a form of addressing in  An instance variable is a variable that is a member of an instance of a class (i.e associated with something created with a new), whereas a class variable is a member of the class itself. Every instance of a class will have its own copy of an instance variable, whereas there is only 1 of each static (or class) variable, associated with the class itself.


Using Class and Instance Variables, GradeBook Class with an Instance Variable and a Property its instance variable courseName, but it's considered good practice for methods of a class to use that class's properties to manipulate instance variables (as we do  Object-oriented programming allows for variables to be used at the class level or the instance level. Variables are essentially symbols that stand in for a value you’re using in a program. At the class level, variables are referred to as class variables, whereas variables at the instance level are called instance variables.