--- title: Move pieces on the board - Implement Chess with Ruby for beginners slug: move-pieces-on-the-board-implement-chess-with-ruby-for-beginners published_at: 2021-05-31 17:00:21 +0000 updated_at: 2026-03-04 20:14:11 +0000 summary: description: In this series of videos you'll learn how to implement a simple terminal based Chess game with Ruby. In this episode we update our board class so that pieces can be moved from one location to another. Playlist: https://www.youtube.com/playlist?list=PLS6F722u-R6LZxh7mvEUvZKshcH6KSNhr Code: https://replit.com/@CJAvilla/chess#main.rb tags: [Implement Chess with Ruby for beginners, Chess with ruby, Chess with Ruby for beginners, Ruby tutorial for beginners] views: 306 author: CJ Avilla url: https://www.cjav.dev/videos/move-pieces-on-the-board-implement-chess-with-ruby-for-beginners youtube_url: https://www.youtube.com/watch?v=urZ8aypeSoU youtube_id: urZ8aypeSoU embed_url: https://www.youtube.com/embed/urZ8aypeSoU thumbnail_url: https://i.ytimg.com/vi/urZ8aypeSoU/hqdefault.jpg type: video --- # Move pieces on the board - Implement Chess with Ruby for beginners *Published: May 31, 2021* *Views: 306* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=urZ8aypeSoU) [![Move pieces on the board - Implement Chess with Ruby for beginners](https://i.ytimg.com/vi/urZ8aypeSoU/hqdefault.jpg)](https://www.youtube.com/watch?v=urZ8aypeSoU) ## Description In this series of videos you'll learn how to implement a simple terminal based Chess game with Ruby. In this episode we update our board class so that pieces can be moved from one location to another. Playlist: https://www.youtube.com/playlist?list=PLS6F722u-R6LZxh7mvEUvZKshcH6KSNhr Code: https://replit.com/@CJAvilla/chess#main.rb ## Transcript hey what's up welcome back in this episode you and i are going to work on moving and taking a piece on the board so this is the this is sort of the next step up so um i think what we want to do is go to our board class and actually make some methods here for taking for taking the piece so we've got our initialize in terms of like organizing the code inside of a class what i like to do is keep we want to keep all of the sort of these macros maybe or whatever you want to call them their class methods that are called the very top then we have a space and then we have all the class methods generally at least this is the way that i do it and then underneath the class methods i'll write my initialize and then i generally will like alphabetize the methods below that that are public methods and then we can put the private methods underneath that we could talk about public private and protected method in a bit but for now let's add a new method here called make or like move piece and we're going to give it a start position and or let's just call it start and end no we can't call it start and end start position and end position and what this is going to do is we're going to figure out like what is the piece that's at the start position and we will try to just decide is the end position in the list of available moves and if it is then we will update the location on the board and we will then update the pieces position okay so we need to do a couple things we need to like remove the piece from the board uh at the current location we need to we need to like place the piece on the board at the new location and we need to like do some sort of validation validate that end pause is in available moves uh what else do we need to do we also need to like update the pieces internal location with the new with the end position okay so let's see so we want to validate the that the end position is in the valuable valid moves so let's grab the piece here and just say self at start pause so that should give us the piece and then we can say like is the um if the piece dot available moves that include end pause or if it doesn't include if it does not include the end position then we probably want to do something maybe we want to raise an exception or print something for now let's just say raise so in in ruby you can you can raise your own custom exception types or you can just pass a string so here we can just say like end position not in available moves now we're going to need to handle this exception somewhere upstream but we can we can talk about that in a bit raising like basically says some exceptional thing happened in the execution of this program and uh we we don't know what to do with it so we're just going to throw it up and then at each function call up the method chain so like wherever we called move piece and wherever that code was called from it'll sort of like build up a stack trace of where each of those methods were called and then print out this this error message so every time your code crashes and you see these error messages um at somewhere down in in the bellies of libraries and other things exceptions are being raised just like this and you can wrap these in begin rescue blocks in order to handle them yourself generally you don't want to like manage can control uh like um conditional logic or flow of a program with uh exceptions but in this case we want to like make sure that the board if you ask the board to move a piece from a start position to an end position that it's it just fails if there are no available moves or if we're trying to move to an invalid spot um the other thing we can check too is that like um if the end position is actually in bounds so if it's not um in inbounds uh end position then we can also say raise like end position not in bounce or something all right so then we want to remove the piece from the board at the current location the way that we do that right now is we're just saying uh n or at the yeah start pause is equal to nil the reason we're able to do this right now is because we have reference already to the start p or to the piece here by setting this equal to nil we are uh we're changing what um the internal grid representation of the board is referencing for that spot in the array we're setting that to nil but that doesn't necessarily like delete the class or anything it's just going to remove that reference now if we didn't like store reference to the piece somewhere then we might lose reference to that piece and it might get garbage collected so because we're already grabbing that up here we should be able to use the piece throughout this entire method without without issue so that's something to keep in mind all right so then we want to place the piece on the board at the new location so we can say like self at end pause is equal to piece and then finally we want to update the pieces internal location with the end position so self our piece dot location is equal to end pause right here we're going to try to set the location of the piece however i don't think we have a setter method for location so right here we're trying to call a method called location equals and pass it in an argument end position but if we look at piece we have an adder reader for the location that so when we have an adder reader that's just def location at location right that's the only method that is added when you use this macro if you wanted to have a setter which is def location equals new position or whatever our new location and you want to set at location equals new location then instead of having just add a reader we want to have the method that or the macro that we can use to create that is adder writer location however there is a there's a shortcut for creating both of these and it's adder assessor and so what we can do is remove location from the reader one and use adder assessor which will create both a getter and a setter so that should help us set and update the location when we're moving it around so now if we go back to our board i think this might work maybe um there's a couple other things that we need to do usually when you're moving a piece like you can't move a piece that will end up moving you into check right and you can't move a piece uh yeah there's a couple there's a couple like interesting things like you can't move a piece onto your own piece and things like that so um we'll start with this and see where we see where we land um if we were to go back to the main here we've got our board set up and then if we try to say like b dot move piece and we pass it the start position maybe we grab the pawn that's here so this is going to give us the pawn at 1 1 and we want to move it to let's say that we want to move it to here and take this piece so we want to move one one two two two and then we'll render out the board and see what happens so let's run it all right so we were able to move that from there to there and there is no longer a white piece there so the black piece that was at 1 1 is now at 2 2 and it was able to take that piece now if we try to move it to like 2 or like 4 4 or something then i think we're going to get an exception which is what we expect because um because 4 4 is not a valid move right okay so and here we see the exception message it says end position is not in available moves great that error message could be improved like you tried to move to an invalids position like you were at 1 1 and here are the valid positions let's actually let's do that so if we go back to our board class end position is not in available moves and then we'll print out the available moves so that they know where they could have moved from oops is not in the available moves which are available moves let's see if that works we might need to do like dot inspect or something to see um okay available moves is on piece and what does this look like great okay so the end position is not in the available okay and we can say like end position and then put in in here like end pause so where we tried to move to is not in the available moves this gives us a much better error message when you're when you're raising exceptions it's it's pretty nice to like experience this as a developer who's working with it where it tells you you know like the end position 4 4 is not in the available moves 2 two three one two two two zero uh if we were building a much more complex uh game here what we could do is um we could actually show on the display of the board like a red mark or something where they tried to move to and then you know yellow marks or something where they could have moved to um so this is this is handy all right so now we've got our piece our piece move sort of logic is somewhat in place and we're able to move around and we're able to take a piece all right so let's go into the next episode and we're going to write some logic for i think the next one maybe we should tackle is sort of just taking turns like walking through um maybe building out the actual game that we will play and as you're playing it we're going to toggle between two different players and we're sort of like take turns entering in which position you want to move from which position you want to move to and then sort of like using those as input to this move piece method here and then we can we can go from there i think we'll save one for a little bit later we need to like add logic around are you in check you know where the king is and it's such like um so yeah let's go let's go into the next episode and talk about taking turns thanks so much for watching and we'll see you shortly --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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