First Class Object at Five Levels

Let’s discuss First Class Objects.

  1. Child: Imagine you have a toy box full of different toys. Some are cars, some are dolls, some are balls. You can play with them in any way you want. You can give them to your friends, you can take them from your friends, you can put them in your toy box or take them out of the toy box. In programming, a ‘First Class Object’ is like a toy. You can play with it any way you want.

  2. Teenager: You know how you can use a calculator for many things like adding, subtracting, multiplying, etc. You can even use the result of one calculation in another calculation, right? Well, in programming, we have things called objects. When we say an object is ‘First Class’, it means we can use it in the same way as any other objects - like the numbers in your calculator. We can pass them around, use them in functions, and even create them while the program is running.

  3. Undergrad: In computer programming, ‘First Class Objects’ are entities which can be dynamically created, destroyed, passed to a function, returned as a value, and have all the rights as other variables in the programming language. Functions in JavaScript are first-class objects, because they can have properties and methods just like any other object. They can be passed as arguments to other functions, and they can be returned from other functions, allowing for a level of dynamic flexibility.

  4. Grad Student: When we talk about ‘First Class Objects’ in the context of programming languages, we refer to entities that can be treated uniformly throughout. They can be created/instanced at runtime, passed as parameters, returned by functions, and assigned to variables. The concept of first-class functions is one of the core concepts that makes JavaScript a very expressive and powerful language, and it enables high levels of abstraction and expressiveness that are used in powerful design patterns, such as functions as first-class objects, closures, and higher-order functions.

  5. Colleague: A ‘First Class Object’ in a language implies that the entity supports all the operations generally available to other entities. These operations typically include being passed as a parameter, returned from a function, and assigned to a variable. In languages with first-class functions, the functions are treated no differently from any other type of object. This opens the door to powerful language features such as higher-order functions and lambda expressions. It allows for techniques such as Currying and facilitates paradigms such as Functional Programming.

Key Properties

What is the term that has the following properties:

  1. They can be bound to names.
  2. They can be passed as arguments to functions.
  3. They can be returned as the result of functions.
  4. They can be included in data structures

First Class Entity

The term that describes entities in a programming language that can be bound to names, passed as arguments to functions, returned as the results of functions, and included in data structures is “First-Class Citizen” or “First-Class Entity”.

When we say that functions are “first-class objects” in a programming language, we mean that they support the operations generally available to other entities. These operations typically include being passed as an argument, returned from a function, modified, and assigned to a variable.

So, in JavaScript and Python (among other languages), functions are considered first-class citizens because they can be assigned to variables, stored in data structures, passed as arguments to other functions, and even returned as values from other functions. This capability leads to a number of powerful programming techniques, including the creation of higher-order functions.

Richard Feynman Explanation

Imagine a small town with a few residents. In this town, you’ve got people, houses, cars, and let’s say, trees. Now suppose we have a town rule that says, “Anything that has a name or can be given a name is considered a ‘first-class citizen.’”

So, a person named John, a house named “The Mansion,” a car named “Speedy,” and a tree named “The Old Oak,” are all first-class citizens in this town. They all have names and can do certain things. For instance, John can own “The Mansion,” “Speedy,” and “The Old Oak.” We can say, “John’s house is ‘The Mansion’.” “John’s car is ‘Speedy’.” And, “John’s favorite tree is ‘The Old Oak’.”

In the world of programming, specifically in object-oriented programming, when we talk about ‘first-class objects,’ we’re really talking about elements that, just like our town’s first-class citizens, can be given names (or assigned to variables), and used in various ways. They can be created dynamically, stored in data structures, passed as arguments to functions, returned as values from functions, and assigned to variables. They can have their own properties and methods.

In short, a ‘first-class object’ is an element in the programming world that has all the rights and privileges associated with being “first class,” just like John, “The Mansion,” “Speedy,” and “The Old Oak” in our small town.