Faking It: Overloaded Operators, Linked Lists and more

Faking It is a series of posts whereby I go to meetups and other tech events, write down a bunch of concepts everyone’s throwing around willy-nilly, figure out what they are, and explain them in basic language. This is the first one, but I’ve been going to tech events for a while now and there are plenty of concepts that go right over my head. All examples are given in Ruby.

Yesterday, I was at the Got Lambda meetup here in Gothenburg. The speaker was going over a functional programming framework, walking us through some of the main features and giving code examples. At some point, I just started writing down a bunch of concepts he was throwing out like everyone would understand. Maybe everyone else did understand. But I figured I ought to figure this stuff out, then maybe the meetups will be more interesting. And if I’m going to figure something out, I might as well write about it. Thus, this post.

I’ve heard all these things before, but I still don’t know what the deal is. Maybe you’re in the same boat.

Overloaded Operators

The general idea here is that you have an operator (+ — / *) that can work in more than one way.3 + 3 is not the same as 3.0 + 3.0 but you can use the same operator (+) because that is an overloaded operator. One adds integers, the other floats — the way the operator works changes based on the arguments. The first one returns an integer (6), the second a float (6.0).

I thought this one would be an easy google, but it wasn’t until this SO question that I understood that while they are saying “overloaded” what they mean is “overridden”. This link is also helpful, but discusses C++.

Linked Lists

I know from my brief work with algorithms that this is a rather large topic, but I wanted a general overview of what this means. At the meetup, the speaker was saying that the arrays were all linked lists. What?

Sometimes Wikipedia gives overly technical answers to my programming questions, but this one was actually very helpful. A linked list is a collection of nodes. Each node consists of a piece of data and a pointer (a “link”) to the next node. As the article explains, one of the main benefits of linked lists is that items can be inserted or removed without needing to reconfigure the entire structure — simply update the pointers for the affected nodes.

Arrays in Ruby have indices and those serve as our “pointers”. If you want to know what is stored in the 3rd item in array, you’ll need to use the 4th index. If you delete the first item, that changes the index of that item. In linked lists, no such rearrangement is necessary: the “index” of items does not change.

Tuples

A tuple (pronounced TUH-pull) is just like an array, but it cannot be changed (it is immutable). Confusingly, they are synonymous with “records” in some languages.

I found this gem that allows you to use tuples in Ruby, but otherwise I don’t think it’s a common or popular thing to do in the language.

Currying

Currying is a functional programming thing that breaks up a function that takes multiple arguments. You then deal with them separately as functions within a function that each take one argument. This tutorial has a great example on currying in Ruby and this one is very helpful for understanding the concepts. I’m using the second as base for an example:

def sentence(string1, string2)
string2 + ' ' + string1
end
def addDude
appendText = lambda do |fn, string1, string2|
send(fn, string1, string2)
end
 appendText.curry.(:sentence, 'dude')
end

There’s some next syntax here for the uninitiated (as I was). send is passing on a “message” of sorts — about the arguments and the function to be called. It is going to pass dude down the line into the curried function. curry and the .(: notation allows for “auto-currying”. We call it with addDude.('yo') and get 'yo dude' in return. We are skipping over the addDude function and passing that variable into the appendText curry construction.

Currying in Ruby

So why would anyone do this? It allows for reuse of functions. So above we are passing a function into appendText.curry.(:function, argument) that could be reused to do all manner of thing to our argument. It allows our code to be dry and allows our functions to be “pure” (produce the same output for the same input). This article was helping for more of the “why” behind this method.

PS: While figuring this one out, I came across that string1 * 2 is “yoyo” but 2 * string1 throws an error (String can't be coerced into Fixnum). Fun!

Ok, that’s it for today! I’ll be back at you with more crazy concepts after future head-scratching at tech meetups.