If we wanted to, we could, of course, write web applications in assembly code. Computers can understand assembly code just as well as Ruby or Python or any other language.

The reason we write programs in higher-level languages like Ruby or Python is that while assembly language is easy for computers to understand, it’s of course not easy for humans to understand.

High-level languages (Ruby, Python, Java, C++, etc.) provide a layer of abstraction. Instead of having to think about a bunch of low-level details that we don’t care about most of the time, we can specify the behavior of our programs at a higher, more abstracted level. Instead of having to expend mental energy on things like memory locations, we can focus on what our program actually does.

In addition to using the abstractions provided by high-level languages, we can also add our own abstractions. A function, for example, is an abstraction that hides low-level details. An object can serve this purpose as well.

We’ll come back to some technical details regarding what abstraction is. First let’s gain a deeper understanding of what an abstraction is using an analogy.

Abstraction at McDonald’s

Let’s say I go to McDonald’s and decide that I want a Quarter Pounder Meal. The way I express my wishes to the cashier is by saying “Quarter Pounder Meal”. I don’t specify the details: that I want a fried beef patty between two buns with cheese, pickles, onions, ketchup and mustard, along with a side of potatoes peeled and cut into strips and deep-fried. Neither me nor the cashier cares about most of those details most of the time. It’s easier and more efficient for us to use a shorthand idea called a “Quarter Pounder Meal”.

The benefit of abstraction

As a customer, I care about a Quarter Pounder Meal at a certain level of abstraction. I don’t particularly care whether the ketchup goes on before the mustard or if the mustard goes on before the ketchup. In fact, I don’t even really think about ketchup and mustard at all most of the time, I just know that I like Quarter Pounders and that’s what I usually get at McDonald’s, so that’s what I’ll get. For me to delve any further into the details would be for me to needlessly waste brainpower. To me, that’s the benefit of abstraction: abstraction lets me go about my business without having to give or receive information that’s more detailed than I need or want. And of course the benefit of not having to work with low-level details is that it’s easier.

Levels of abstraction

Even though neither the customer nor the cashier want to think about most of the low-level details of a Quarter Pounder Meal most of the time, it’s true that sometimes they do want to think about those details. If somebody doesn’t like onions for example, they can drop down a level of abstraction and specify the detail that they would like their Quarter Pounder without onions. Another reason to drop down a level of abstraction may be that you don’t know what toppings come on a Quarter Pounder, and you want to know. So you can ask the cashier what comes on it and they can tell you. (Pickles, onions, ketchup and mustard.)

The cook cares about the Quarter Pounder Meal at a level of abstraction lower. When a cook gets an order for a Quarter Pounder, they have to physically assemble the ingredients, so they of course can’t not care about those details. But there are still lower-level details present that the cook doesn’t think about most of the time. For example, the cook probably usually doesn’t think about the process of pickling a cucumber and then slicing it because those steps are already done by the time the cook is preparing the hamburger.

What would of course be wildly inappropriate is if me as the customer specified to the cashier how thick I wanted the pickles sliced, or that I wanted dijo