--- title: Building a Board class - Implementing Chess with Ruby for beginners slug: building-a-board-class-implementing-chess-with-ruby-for-beginners published_at: 2021-05-27 01:32:58 +0000 updated_at: 2026-03-04 20:14:11 +0000 summary: description: In this series, you'll learn how to implement a very basic terminal based Chess game in Ruby. In this episode, you'll learn about: * Operator overloading * The convention of adding a `?` to the end of methods * Getter methods with `attr_reader` * Passing tuples rather than x and y for coordinates Playlist: https://www.youtube.com/playlist?list=PLS6F722u-R6LZxh7mvEUvZKshcH6KSNhr Code: https://replit.com/@CJAvilla/chess#main.rb tags: [Building a board class, Building a Chess Board in Ruby, Chess in Ruby, Chess in Ruby for beginners, Implementing Chess in Ruby for beginners] views: 2707 author: CJ Avilla url: https://www.cjav.dev/videos/building-a-board-class-implementing-chess-with-ruby-for-beginners youtube_url: https://www.youtube.com/watch?v=Zc0ZuH3Qpxw youtube_id: Zc0ZuH3Qpxw embed_url: https://www.youtube.com/embed/Zc0ZuH3Qpxw thumbnail_url: https://i.ytimg.com/vi/Zc0ZuH3Qpxw/hqdefault.jpg type: video --- # Building a Board class - Implementing Chess with Ruby for beginners *Published: May 27, 2021* *Views: 2707* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=Zc0ZuH3Qpxw) [![Building a Board class - Implementing Chess with Ruby for beginners](https://i.ytimg.com/vi/Zc0ZuH3Qpxw/hqdefault.jpg)](https://www.youtube.com/watch?v=Zc0ZuH3Qpxw) ## Description In this series, you'll learn how to implement a very basic terminal based Chess game in Ruby. In this episode, you'll learn about: * Operator overloading * The convention of adding a `?` to the end of methods * Getter methods with `attr_reader` * Passing tuples rather than x and y for coordinates Playlist: https://www.youtube.com/playlist?list=PLS6F722u-R6LZxh7mvEUvZKshcH6KSNhr Code: https://replit.com/@CJAvilla/chess#main.rb ## Transcript so if you're just starting out and you're writing some ruby code and you want to learn some object oriented basics one of the best ways that you can do that is to build some games so in a previous episode we talked about building hangman which is a pretty simple game we looked at both the the way that you might write it just sort of by calling functions and passing some data around with local variables and then we built it into a single hangman class where you could just call methods on the instance of the hangman class and those would result in playing the actual game and so what i wanted to do now was really step it up not one notch but two or three notches here and walk through the process of building out chess so this is going to be a series of videos and if you follow along then you'll be able to at the end build a very simple chess game we're not going to uh probably won't implement things like ompassant or like crazy um like intense chess moves but the goal is that we'll be able to build out a very simple chess game with pieces that we can move around a board and we'll have two players and some really basic logic for checking if the game is over or not i'm not a huge chess player i've i know some basic rules of the game but i do think that this is a really effective way to learn object oriented programming and so in this first section what i think it makes most sense to do is just talk about how we organize our code in a project like this and so i'm looking at replit right now and i do want to build it on replits so that you can sort of take uh take this uh resulting code and go play with it yourself and experience it yourself all right so the very first thing that i usually do is add a lib directory and in the lib directory this is kind of the library where all of our code is going to to live and then we want to create one file per class so a class in an object-oriented programming is a type it is going to be sort of the the prototype or the blueprint for instances of that type so you can sort of think of this as blueprints for the um the types that you're going to create this is going to be the list of the methods that are available and this is also where we sort of define how the logic works for each sort of instance of those classes so let's let's dig into it here so the very first thing i want to make is probably a board class so i'm going to call board.rb here and in our board class we're going to start it with class and board and the name of our classes are always going to be capitalized that is a special thing in ruby and we're going to start with class and just an end at the bottom now in between the class where we define the name and the end this is where we're going to write all of our instance methods class methods and where we're going to actually write the logic for what the board is responsible for and so one way that folks often learn object-oriented programming is to think about the nouns in their system as the classes and then you think about like the verbs as the methods or like the actions that are happening between those classes that's sort of like classical object oriented programming now one book that i highly recommend is called pooter it's like practical object-oriented uh ruby practical object-oriented design in ruby this is written by sandy metz very very good book um really well written and has some really really strong object-oriented principles and design methodologies that are really valuable so i definitely recommend checking out this book pooter by sandy metz and what she does is she sort of flips it on its head and says first think about the um the messages that you're going to be sending between the actors in your system messages and this is really sort of like the methods that you're calling and then you have like the secondary thing is like the actors or this is going to end up being your classes but you don't have to really think about the classes until first you think about how the messages or which messages are most important in your system so these are kind of two different ways of approaching it i uh learned the the first way where you kind of like think of all the different nouns in your system and then create classes around those both are totally valid the one thing that you want to keep in mind is that a class very often should be responsible for one thing the single responsibility so this is a board class and it's pure responsibility is going to be managing the board so we're going to try our best to keep it just to managing the board and in practice you might even create like special classes that are specific to rendering the board initially we're just going to assume that some other class is going to actually render out the board but what do we want the board to look like so i think this should actually be stored as sort of like a 2d array where the the rows are going to be the index into the array then the columns will be some position in a subarray so we're going to have sort of like arrays of arrays right where like the top level array will give us like the rows and then the sub arrays will give us columns and then at each point we can have like a piece either a piece or a nil and so we'll have sort of an eight by eight two by two or i'm sorry i love an eight by eight two d array that is the internal representation representation of the board so here let's say def initialize and we're going to say like the internal representation we'll call it the grid just to keep it just to keep things separate now what we really want to do here is initialize this with a 2d array and we can do it a couple different ways like first of all what we could do is have a method that like sets up the whole board and actually like creates the pieces and puts them on the right places on the board or we could inject the grid into the board when the board is initialized but i think what we might want to do is to start let's just put in let's just put in like x x nil and x and what we're going to try to do is sort of get something working um so that we can just see what this looks like on the board we don't even have like the right dimensions yet we'll just make it four by four to start and then we'll start playing around now what are what are some things that we might need to do on the board or with the board right so um a couple things that come to mind we're going to want to like place pieces um and we're going to want to like have a way to check to see if we're out of bounds um we're going to want to probably have methods for for getting or retrieving a piece at a specific position so like get a piece and then there's likely other things but let's start with that so um if we wanted to place a piece one thing that we might do is write a method that's called like place and then it takes in a piece and maybe it also takes in a location where the location is going to be like some pair of x y so we might we might expect that this place method ex takes in the piece object as the first argument and then an x and then a y or maybe like even like row and column or something right and then we can um find that row and column in our grid so i i put an at sign at the front of this this name here grid i put the add sign because this is going to be an instance variable meaning that every time we create a new board each board should have its own internal representation we don't want the boards to all share the same internal representation so for instance if i say like b equals board dot new b dot place and then i give it a piece king and then it's going to go to like one two as the position and if i have a separate board right so imagine that like i'm sitting at a dinner table and on one side of the table i have board that's b and then on another side of the table i have like b2 is board dot new and b dot place the king on zero zero these are actually going to be two different boards so i'm sitting at the dinner table i have two different boards right and their internal representation of the pieces on the board b so this b one right or b has a king a position one two and then b2 that's over here is going to have a king at position zero zero and because i'm using the at sign um when we call this or when we're working with our with our board objects they will have this this grid instance variable is going to be an internal representation of the board of like where the where the data is stored for that board all right so we've got this place method maybe it takes a piece maybe it takes a row and column and then perhaps it's going to say like at grid at row and at column and then that's going to actually set that equal to the piece right so this is this is an example of how we write we might write a p a place method so let's let's do a little bit of refactoring the very first thing i want to do is other than the initialize method i want to try to sort of avoid using the instance variable directly instead what i want to do is use the bare word version of the instance variable and in this case what we can do is we can we can use adder reader and give it a grid and this will create a method so by using add a reader here we're actually defining a new method grid that just returns the the instance variable grid so these two line are like this line here line two and then lines four through six those are functionally equivalent they're the same thing they do exactly the same thing this one is just a shortcut it's just a sort of it's called syntactic sugar it makes it easier to read and this is such a common thing that we're going to do that this makes it easier so the first refactoring that we want to do is we want to avoid using this the instance variable directly and instead we want to use grid and the reason is that if later on we decided that every time we access the grid we actually want to do something else or if every time we access the grid we want to make an api call or we want to send an email or something like that then our def grid method we can still return at grid at the bottom but first we could do something here do something right and then we have just uh and then we could just comment this out right like if later on we wanted to like do something every time the grid method was called then we could do that here do something right and by ref by making that small refactor where we just remove the adder reader and we add a new getter that still returns the instance variable but it also does something it makes that type of refactor very easy and so that is one of the reasons why we want to use what's called the bare word instead of using the instance variable when we're working with with our classes here so i'm going to comment that back in alright so we've got this grid so every time we call the grid method we're sending the grid message to ourselves and we're getting back this 2d array which is the internal representation and then we're reaching into its row which is going to be like picking which of these arrays to use and then the column which is which element in the array and then we're going to set that equal to the piece um so a couple of things number one rather than passing around row and column because we're going to be working with this this uh locations on a grid very frequently or locations on the board very frequently within the game of chess right we're gonna have like positions where where a piece can move right like a um a knight and a rook have like certain directions they can move and certain pieces that are able to move in different directions uh those directions will also be defined as these sort of pairs of x and y which allow you to move forward or move backward or move side to side and so because the pairing of the row and column or the pairing of the x and y is so common instead of passing those as separate arguments it is a better practice to pass them as a single thing a single argument so we can just say location here and instead of uh passing in row and column to the method we can extract the row and column from the location using array destructuring like this row comma column is equal to location and that will just automatically sort of destructure the array so if we receive a piece i'm sorry if we receive a mess a message that place message with a location so now this is going to look a little differently now we're going to have b equals board dot new b dot place like king somewhere and then instead of passing one and two we're gonna pass them as an array one comma two now in practice we might actually even create a location class that is like purely responsible for validating that a location is legit and like you can't have negative locations and you can't have whatever um but for now we're going to keep it really simple and every location will just be passed around as a a single element or i'm sorry a single array with two elements so that's what that's what our sort of uh location will look like now um if you've worked with arrays before and um i'm hoping that's sort of like a prereq to this but um if we have an array a and it looks like this and has one two three elements in it and you ask yourself how do i get the first element out of this array well you might say like puts a at square brackets zero right or alternatively you might say puts ada first but what i wanted to talk about was this square bracket thing that we've seen elsewhere right so in this case a itself is an array but when we are looking at the first index here this this square bracket when the square bracket is right next to a this is actually calling a method on a and the method is a special kind of method and that method is the square bracket operator so this is a special kind of operator the same way that like you might have like one plus two this is actually a method one or the the plus method here is a method so um a at zero is a method so let's try running let's actually move this into main here so we can run that and just take a look at what it does so i'm going to i'm going to run this and we will see that if we put out 0 we should see one print to the console and we do so what's interesting is you can actually i think you can put a dot here because it is like calling a method and the method is the square bracket operator um okay let's see maybe i need to call it like this okay look at that all right so we we get back one we still get back one what's so interesting here is that this dot square brackets is the is the method in this method is the getter method it's the method that is like extracting something from our 2d array all right now this is where it's going to get even more interesting is that if we say puts a down here we can actually use the setter method right so typically typically if we wanted to change the value at index 1 let's say we want to set the the value of index one to just like test right and then we're gonna put out a it's gonna say one test three that's what we expect so this here is okay so now we see one test three it's not printing it in array status because we're using puts so it's making it pretty but this is also a method so the square bracket operator we pass it the index of the thing we want to set and then we have this equal sign on the right side this is another method that is available on array so it turns out that we should be able to also call a dot square brackets equals and then call this with two arguments the first is going to be the element we want to change so let's actually change three to test now so it says one two test right so this is the index into the uh into the array and then this is the argument that we wanna set the value for so here we're calling the method and we're calling it with parentheses because we want to set the value i'm sorry we're not it doesn't matter the parentheses part doesn't matter the set value is because we're as we're calling the square bracket equals operator instead of the square bracket operator and we're able to pass it these two arguments and that ends up setting it so what why does any of this matter what what's the deal well it turns out that like when we're defining our own classes we can do what's called operator overloading so we can change what it means to uh both retrieve and set values on our custom board class so let's do that because i think that's pretty cool so here instead of our place method let's make this the square bracket equals method and then we want to actually swap the order of these so that the location comes first and the and the piece comes second now when we go to call this method we're going to call it by passing in first the location so we're actually going to use the square bracket operator we're going to say location and then equals king or whatever our piece is going to be so then the location is going to be like you know one comma two and now we can use this setter method just like this to set the value at that location let's just pass in like y for now and then we can print out b uh dot grid we'll just make it like print out the whole grid so that we can take a look at this so let's actually move this up to main and we will require require relative dot slash lib slash 4.rb we're going to initialize a new instance of the board we're going to create a location and use that setter method to take this value and put it on to the location at one two actually let's use zero zero so it's a little bit easier to see where it came out and now we see that in location zero zero we have a y instead of an x okay so this is the center method i think this is pretty cool um so this is uh the setter method so again similarly we can use this for get so we'll just copy this and paste it down here and the difference between get and set is with get we only need to take in the location we don't actually need to pass a piece and then we're just going to return the value at that location so now if we go back to our main class here if we were to say like print out be at location then we should expect that this prints out y right so we will run that and we get back why super cool so i've kind of done something a little fun here because i've created the this loc for the location this local variable that has our 2d array but if we were to like actually do this with um with an inline sort of like uh array that we're just defining here we might say like be at like what is what is the value of b at um location 1 1 and this is super weird to kind of look at because it has two sets of square brackets around it but this is actually valid also so we can print out what what do we see at location 1 1 and we actually see x and that's i think that's that's also expected so we could just say like uh p b grid and that should give us a better look here so at location 1 1 we're looking at the first arrays first element here so that's one one if we did one two i think that should give us nil so let's take a look and we got nilback that's great so this is kind of a couple of convenient methods that we have on board now let's let's make another method here called out of bounds and this will also take in a location and what we're going to do is uh again destructure into row and column and we're going to check is the row less than grid.length and is the column less than grid dot first dot length and i think that should be like pretty close we actually also want to check to make sure that that they're greater than zero so we can do that so rho is greater than or equal to zero and um and column is greater than or equal to zero so this should tell us whether or not a location is out of bounds based on what our current and like internal representation is what's neat about this board class so far also is that it's four by four which isn't a technical like chess grid but it should still like work in pretty generic ways right like we could use we could reuse this board if we wanted to with a tic-tac-toe board or we could reuse it for checkers or chess or a couple other like grid based boards um and that should totally work as expected and then here what we might do is say like uh b um we'll print out a couple things so we'll just say like b dot out of bounds is it out of bounds to go to like uh negative one zero that should be true um or maybe we should call it inbounds inbounds right because we said less than less than greater than yeah so this is inbounds so if it's inbounds and then let's give it a valid one so zero zero let's also give it like one one and then we'll go over and above so in our case like our temporary one is just a four by four so that should fail so we should have yep it's not in bounds it is in bounds it isn't bounds and it's not inbound so that that works that's totally cool and so now we have a board class that has a couple of methods on it that i think should be really helpful so i'm going to wrap this episode right here we talked about how to create a class and how to put it in the right file we talked about these instance variables and why we want to initialize and set the instance variables inside of the initialize method but then later on we only want to use the bare word to access them we talked about operator overloading and passing in locations as the the pair or the tuple of the x and y uh and we built a couple different methods here this one in particular i like having the question mark at the end that's sort of a convention when you're returning a boolean value so again here at the end this is sort of like a multi-line expression where we're putting the ampersands at the end so we're evaluating each of these uh in order um and then returning the whole result of this entire thing which tells us whether or not we're inbounds yeah we talked about yeah how you generally start thinking about these uh object-oriented systems with nouns and verbs versus messages and and methods so hopefully this was useful if it was i'd really appreciate a quick like and uh yeah in the next video we'll talk about some other part of the chest system we'll continue building this up thanks so much for watching we'll see in the next one --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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