---
title: Creating classes for Chess Pieces - Implementing Chess with Ruby for beginners
slug: creating-classes-for-chess-pieces-implementing-chess-with-ruby-for-beginners
published_at: 2021-05-27 22:41:44 +0000
updated_at: 2026-03-04 20:14:12 +0000
summary: 
description: In this series, you&#39;ll learn how to implement a basic terminal based Chess game with Ruby. In this episode we create the piece classes for Pawn, Rook, Knight, King, Queen, and Bishop.   We cover: * Ternary operators * Why use Symbol vs String * Duck typing - using the same method name across similar classes * Waiting to DRY up code until the system is well known  Playlist: https://www.youtube.com/playlist?list=PLS6F722u-R6LZxh7mvEUvZKshcH6KSNhr Code: https://replit.com/@CJAvilla/chess#main.rb
tags: []
views: 989
author: CJ Avilla
url: https://www.cjav.dev/videos/creating-classes-for-chess-pieces-implementing-chess-with-ruby-for-beginners
youtube_url: https://www.youtube.com/watch?v=-wLVmf7-efU
youtube_id: -wLVmf7-efU
embed_url: https://www.youtube.com/embed/-wLVmf7-efU
thumbnail_url: https://i.ytimg.com/vi/-wLVmf7-efU/hqdefault.jpg
type: video
---

# Creating classes for Chess Pieces - Implementing Chess with Ruby for beginners

*Published: May 27, 2021*
*Views: 989*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=-wLVmf7-efU)

[![Creating classes for Chess Pieces - Implementing Chess with Ruby for beginners](https://i.ytimg.com/vi/-wLVmf7-efU/hqdefault.jpg)](https://www.youtube.com/watch?v=-wLVmf7-efU)

## Description

In this series, you&#39;ll learn how to implement a basic terminal based Chess game with Ruby. In this episode we create the piece classes for Pawn, Rook, Knight, King, Queen, and Bishop. 

We cover:
* Ternary operators
* Why use Symbol vs String
* Duck typing - using the same method name across similar classes
* Waiting to DRY up code until the system is well known

Playlist: https://www.youtube.com/playlist?list=PLS6F722u-R6LZxh7mvEUvZKshcH6KSNhr
Code: https://replit.com/@CJAvilla/chess#main.rb

## Transcript

hey you&#39;re back i guess you wanted to learn more about chess maybe all right so uh in the last episode we talked about building out this board and uh operator overloading in this episode we&#39;re going to start building up pieces so let&#39;s talk about how we might build a piece class so i&#39;m going to add a new file i&#39;m going to call this oh should we do pawn let&#39;s do pawn first so pawn.rb is going to be our first piece so i&#39;m going to call this class pawn and there&#39;s a couple things that are unique to each piece uh that uh in chess right one is the types of moves that each piece is allowed to make so a pawn is the most basic piece it&#39;s on like the front row uh when you start playing and it is allowed to either move forward two spaces or move forward one space and so what i think we want to do is define some sort of like directions that a piece is allowed to move so move dirs maybe is like the move directions uh and then yeah let&#39;s start with that so let&#39;s say that our our pawn has some like directions that it can move so let&#39;s make a new method called move dirs and initially we will just make this return an array where each element in the array is the directions that it can move so i guess if it can move only in it can only move in the y direction right up and down it can&#39;t move in the left and right directions so i think it can move um it can just move forward and and to start let&#39;s just say that a pawn can only move one step forward we&#39;ll just save the case where it can move two steps because we need a little bit of logic around like is it at its starting position and if it is then like moveders is different um so let&#39;s actually let&#39;s let&#39;s figure that out so if if the pawn is at its starting position so um starting starting position maybe starting pause and we&#39;ll say like if ah interesting so does it need to have a location so should each piece maintain reference to its own location this would be helpful if we were looking at is it in the starting position right so should each piece have its own location let&#39;s let&#39;s just start off with um an initialize method here that has the location so we&#39;ll say at location is location so maybe we do want to store the location in each piece i don&#39;t know we might come back and adjust that i&#39;m not sure but let&#39;s let&#39;s just assume that we start off each piece and it maintains reference to its location that that way what we can do is we can say um we can say we can actually make a couple of getters here row and uh column column and we can say column is at location dot last and row is at location.first let&#39;s actually put these at the bottom here and then we could say if the row is equal to 1 or the row is equal to what is going to be the other side six maybe um then it&#39;s at the starting location um and i think that will work right because of oh let&#39;s see chess chess board uh is a chessboard 8x8 right uh chessboard let&#39;s see yeah it&#39;s eight by eight and if it&#39;s in the starting if it&#39;s in the starting row on this side then it&#39;s going to be in position it&#39;s going to be on the second row if it&#39;s on the um the starting position on this side it&#39;ll be on row seven and what&#39;s neat about the pawn is that you might think like okay well um if we if we&#39;re using this starting position to define whether or not the move directions is one or uh if it has more directions then we might run the risk of like as soon as a pawn starts here and moves its way to the seventh uh the seventh row then it will also be able to move two spaces forward but once it gets to the seventh row it can&#39;t move two spaces forward anyway so it&#39;s kind of like a little bit of a accidental nice thing um so what we want is we want the move directions to return this unless it&#39;s at the starting position in which case we wanted to move we want to return uh like zero and two i think um or maybe we should have like valid all right i&#39;m sort of figuring this out on the fly sort of figuring it out on the fly so the move directions it can move in that direction but we also want it to be able to move in that direction like a certain number of steps um all right let&#39;s let&#39;s save that and come back because we&#39;ll we&#39;ll need to like do a little bit of logic here to figure out what we need beyond beyond these move directions uh in order to make it step only one forward or or multiple forward let&#39;s make another piece and just kind of uh one of the things that we might want to do or what what you should do is when you&#39;re building object-oriented code is to um wait to merge things into a parent class or into a module until you have several where it&#39;s like very very clear that you want to dry things up so dry is don&#39;t repeat yourself dry don&#39;t repeat yourself so we don&#39;t want to we don&#39;t want to like dry up the code too quickly so let&#39;s add another file here we&#39;ll call this one i don&#39;t know rook dot rb and a rook is going to be class rook and a rook is what is a rook a rook is the piece that can move up and down right let&#39;s see chess rook um yep so this is the this is the rook piece and the rook is the piece that is allowed to move on the chess board either it can go up and down or you can go left and right okay so what we&#39;re going to do is we&#39;re going to come back over here we&#39;re going to say def move dirs and we want the names of the methods to be the same across all pieces and the movers for a rook is going to be we can either move in the zero one direction same as pawn or we can move in the one zero direction which is x and y right so like the if we were able to move in i guess you know what we could also move in zero yeah okay so there&#39;s there&#39;s four directions technically that we can move in so this gives us the forward direction we also need to be able to move in the backward direction that&#39;s like going down so we can go negative one and then we also have this one is going to go right and then this one will go left so these are all the directions that a rook can move and let&#39;s see so the other thing that we wanted is probably like some string representation of what the class looks like so one thing that we could do right is if we have a pawn here let&#39;s let&#39;s uh require the pawn here so we&#39;ll say pawn and let&#39;s do the same thing with rook and then we&#39;ll comment all this out and say like p is pawn dot new and then if we say puts p then that&#39;s going to be like the the representation of the pawn is going to be this this is going to be the string representation of the pawn and i&#39;ve got some issue here in rook so i&#39;m looking at this error message and when i look at the error message i am seeing i want to look for the line where the error happened so i see home runner chess lib rook so i know that it&#39;s in the rook.rb file and then this colon here the colon tells you which line number it&#39;s on so i know exactly where i need to look in in the rook class on line eight so i&#39;m gonna go to rook line eight and i see that there is no comma here so that is probably the issue all right initialize wrong number of arguments oh we didn&#39;t pass anything in let&#39;s say the location is zero zero and then we&#39;ll print out puts p all right so this is right now the string representation it says like the class name colon i think this is like the memory address it doesn&#39;t really matter but like this is definitely not what we wanted to print out like probably when we when we display the pawn so when we call put puts or put s this is going to this is actually calling dot 2 s under the under the hood right so if we call puts p 2s we&#39;re getting the same exact result back now if we say p oh gosh okay so it still worked okay so p is a method i don&#39;t know how this is how it knows even though i over i sort of overwrote it but here we go so p pawn.2s so you can see the quotes around it this is the string representation what we can do is we can actually override 2s so we can say def 2s and we can make this whatever we want and i think there might even be a pawn class in nice so there&#39;s a pawn class in the emojis all right so now if we run this we should get back the little pawn it should print out a pawn and it totally does okay i think there might even be like a color so there&#39;s like yeah okay so there&#39;s a black one and there&#39;s a white one and we need to figure out like what color the piece is so we might also take that in color so we say add color is equal to color and then we can say like if color is equal to black then we want to print that string otherwise we want to print this string so this is a ternary operator and i&#39;m comparing it with a symbol okay so now what 2s is doing is it&#39;s it&#39;s evaluating the this expression on the left first and it&#39;s saying is the color um or is at color so we need an adder reader or color so is the color black this symbol black and if so print out this thing otherwise print out this thing okay so why am i using a symbol here instead of something else like we could we could have just as easily used a string or something else the nice thing about using a symbol is that uh internally when you&#39;re running the program there&#39;s only going to be one instance of that symbol otherwise like every time we reference this string here it&#39;s going to create a new instance of a string so it&#39;s just a little bit memory a little bit more memory efficient to use a symbol instead of a string when we&#39;re going to do comparisons like this because it doesn&#39;t need to allocate a brand new string object to do the comparison we&#39;re getting like two into the wheat don&#39;t worry about that let&#39;s go back to our board or back to main and we&#39;ll pass in black here and then we&#39;ll make another pawn here that&#39;s like uh white and then we can print both of those out and we&#39;ll see if it prints out the black one and then it prints out the white one okay so that&#39;s gonna be our black pawn that&#39;s gonna be our white pawn and where this gets really cool is that we can say like we can call b equals board dot new and then we can say like b at index 0 0 is equal to this new pawn which is black right actually or maybe uh one zero and then we can do the same thing for like one one one two 1 3 and then when we print out the board we can say whoops p b grid and then we should see those on the grid and we don&#39;t because we are using p which is inspect so if we say put b grid okay we&#39;re going to need to figure out how to make our board print out like in a square here pretty soon okay so we do we definitely see those black those black pawns uh and if we make one of them white then we&#39;re gonna see some black and some white pawns or one white pawn here at the bottom and we do all right so let&#39;s um that&#39;s okay that&#39;s fine this this is working well for now i don&#39;t i don&#39;t know i&#39;m not like 100 sold that we need to pass the location in but let&#39;s just keep going we&#39;re going to want our uh our initialize meth here our initialize method here to take in the color i&#39;m going to i&#39;m actually going to remove the location from pawn oops what is this got it files pawn i&#39;m going to remove the location here and we&#39;ll come back and work on that later if needed i think the location we should just store it on the board and so we&#39;ll only pass in the color so we&#39;re going to take our pawn it&#39;s going to have an adder reader for color and that&#39;s going to be what we receive and then we&#39;re going to store that as an instance variable color is color all right so we&#39;ve got sort of the directions of these pieces let&#39;s uh let&#39;s get another piece built here add a file for a night okay so class night and this thing is going to be let&#39;s see actually yeah we can just kind of like grab pawn and drop it into night we have the same color this is going to be now the black knight and the white knight so we have knight all right oops nope that&#39;s not it oops um the black knight and the white the white oops knight the white knight okay the knight is the the horsey the horse okay so the directions that a a knight can move in so a knight can move in four directions it can move uh in the l shape i think right so maybe it might be more than four even so it can move like 1 2 or what else can it move it can move 2 1 and it can move the combos of those so and i think that gives us all of our possible moves um for a knight and for now we&#39;re just hard-coding them there&#39;s probably clever ways to like make some sort of array method that ends up like printing these out but um keeping it super simple for now all right so we&#39;ve got our knight what else do we want we want to add a file for king.rb and we&#39;ll say class king one two three four five six seven eight i think that&#39;s right okay cool uh whatever we&#39;ve got our king what else do we need we need a bishop and the bishop is similar to the rook except that the bishop is going to go diagonal instead of instead of left and right and so i believe this one only has four and it&#39;s going to be yeah fantastic all right so we&#39;ve got our colors we&#39;ve got okay bishop what are we missing we&#39;re missing one oh the queen of course the queen autophile queen.rb and the queen is able to move in all the directions that a king of the rook can move and the directions that a bishop can move copy those into queen and add these here so actually i think a queen and a king can move the same the same directions let&#39;s just copy from king we also need i noticed i didn&#39;t have one of our pieces doesn&#39;t have a 2s yet all right so queen um oh that&#39;d be fun right to do like a colored emoji uh okay queen and okay and we&#39;ve got all the movers all right so let&#39;s go back through this we&#39;ve got a bishop we&#39;ve got a board we&#39;ve got a king we&#39;ve got a knight we&#39;ve got a pawn we&#39;ve got a queen and we have a rook that doesn&#39;t have any 2s so let&#39;s finish this out all right i don&#39;t know if i&#39;m going to speed this part up i might speed this up we&#39;ll see okay all right so at this point what i think we want to do is um improve our board class so i think we i don&#39;t know like at this point we&#39;ve set up our pieces we want to improve our board class so that it&#39;s actually set up with the pieces in the right positions and it&#39;s printed out so that it looks like reasonably okay when it prints out and not just in a line and not just like sort of ins with the inspected pieces in it so that&#39;s what i think we&#39;re gonna do in the next episode but uh thanks for sticking with with me through this episode i think we might also potentially break out um and add some logic to the pieces for are they sliding pieces or are they stepping pieces well and like what are the valid moves that are available for a given piece for a given position or something so uh come back and we&#39;ll do that in the next one thank you so much for watching hopefully you&#39;re finding this valuable if so i would really appreciate a quick like maybe even a subscribe if you will otherwise we&#39;ll see in the next one thanks so much for [Music] watching

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