If you’re new to object oriented programming, a natural question to ask is: what does instantiation mean? Like many other concepts in the development world, instantiation is actually a relatively straightforward concept that suffers from having an overly complex name.

What Does Instantiation Mean: A Real World Example

Before we dive into the code, let’s analyze a real world example of instantiation. (And a quick spoiler alert. If you understand what it takes to build a house, you already understand instantiation.)

Let’s imagine that you’re building a house. One of the first tasks you’d most likely do is build a blueprint for the home. This blueprint would contain attributes and features of the house, such as:

• The dimensions for each room
• How the plumbing will flow
• And essentially every attribute/feature of the house

Now let me ask a dumb question. Is the blueprint of the house the actual house? No, it simply lists out the attributes and design elements for how the home will be created.

So after the blueprint is completed, the actual home can be built. Dare I say that the home can be “instantiated”?

Connecting the Dots

From an object oriented programming perspective, a class is the blueprint for an object. A class simply describes what an object will look like and how it will behave.

Therefore instantiation is the process of taking a class definition and creating an object that you can use in a program.

Still a little fuzzy? That’s fine, let’s look at a code example.

Instantiation Code Example

For this example we’re going to have an Invoice class. Inside the class definition we have attributes, such as a customer and total. Along with some behavior, such as printing out an invoice summary.

class Invoice
  attr_accessor :customer, :total

  def summary
    puts "Invoice:"
    puts "Customer: #{customer}"
    puts "Total: #{total}"
  end
end

Implementing Instantiation

Now that we have our class definition, we can create a new instance of Invoice and store it in a variable, as shown here.

class Invoice
  attr_accessor :customer, :total

  def summary
    puts "Invoice:"
    puts "Customer: #{customer}"
    puts "Total: #{total}"
  end
end

invoice = Invoice.new

I have used instantiation to:

• Take a class.
• Build an object based on the class definition.

And with this process in place I can use the object to perform tasks, such as setting the values of the attributes and accessing the methods.

class Invoice
  attr_accessor :customer, :total

  def summary
    puts "Invoice:"
    puts "Customer: #{customer}"
    puts "Total: #{total}"
  end
end

invoice = Invoice.new
invoice.customer = "Google"
invoice.total = 500
invoice.summary

Running this code will give us the following output:

Invoice:
Customer: Google
Total: 500

So, at it’s core, instantiation is the process of taking a class, and creating an object from it that you can actually use in your program.