--- title: send in ruby slug: send-in-ruby published_at: 2021-01-21 00:00:17 +0000 updated_at: 2026-03-04 20:14:33 +0000 summary: description: Send is a way to dynamically call different methods on an underlying object at run time. It allows you to define methods that are more flexible. Code: https://gist.github.com/cjavdev/9900f55c2a31c2dee1a99d29c4ba214e Presenter: CJ Avilla - https://twitter.com/cjav_dev tags: [ruby, metaprogramming, tutorial] views: 1720 author: CJ Avilla url: https://www.cjav.dev/videos/send-in-ruby youtube_url: https://www.youtube.com/watch?v=cY-wxg5z5bA youtube_id: cY-wxg5z5bA embed_url: https://www.youtube.com/embed/cY-wxg5z5bA thumbnail_url: https://i.ytimg.com/vi/cY-wxg5z5bA/hqdefault.jpg type: video --- # send in ruby *Published: January 21, 2021* *Views: 1720* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=cY-wxg5z5bA) [![send in ruby](https://i.ytimg.com/vi/cY-wxg5z5bA/hqdefault.jpg)](https://www.youtube.com/watch?v=cY-wxg5z5bA) ## Description Send is a way to dynamically call different methods on an underlying object at run time. It allows you to define methods that are more flexible. Code: https://gist.github.com/cjavdev/9900f55c2a31c2dee1a99d29c4ba214e Presenter: CJ Avilla - https://twitter.com/cjav_dev ## Transcript what's up everyone i wanted to quickly run through send in ruby ruby's send method often used in you know some meta programming in ruby so send is a way to dynamically call different methods on an underlying object at runtime so you can just pass in the symbol or sort of like the yeah the symbol value for what the name of the method is and uh execute that method so it allows you to run or like build methods that are a little bit more dynamic and flexible but under the hood it's actually quite simple it's just like a way to call a method so if we have um here let's just put or put s we'll print out the result of one plus two right like every rubyist has run this okay so i'm going to say ruby and then this file here meta dot rb so we get the output the number three and so we're saying one plus two it turns out that the way this works is we're actually calling the plus method on the one objects or the the one instance of an integer so if we wanted to we could actually rewrite this with the parentheses and the method call like so so we can use the dot operator to specify which method we want to execute and then the parentheses to specify that we're passing in an argument so this is calling the plus method on the one object so if we run this again we get back the same result another way to write this is send and then we give it the symbol which is which represents the name of the method that we want to call in this case the plus method so we're saying one and then we're calling the send method on the one object and this is built into ruby objects and we're passing the symbol so the symbols in ruby start with a colon so we're sending the plus symbol so this will execute the plus method and it will pass the two as an argument so we can run this again and we get back three so this is this is pretty cool okay so one place you may have seen something like this is when using inject so if we are going to you know sum some integers you might have seen inject used like this where you can pass in some initial value this is our accumulator and then second we often will pass you know a block with some some value for each element in the array and then we'll say like l plus accumulator and return that value so we usually get uh acc here so this is a common way to write the sum write sum but with inject it turns out that if we're just calling the plus operator or the plus method on element and passing in the accumulator or vice versa accumulator plus element then rather than writing out this entire block and telling inject what it needs to do you can actually just do this shorthand where we pass the method and then the method will be applied to each element in the list so if we run this again we again get back 10. so this is kind of like somewhere that you it feels a little bit like send and the way that we would implement inject would be with uh with with send likely right because we want to be able to take in some operator here okay so suppose we wanted to build some message object that had a subject and then some content and then we wanted to construct some resulting representation of that message that is just a you know text value so one way or we can start off with by defining a new class here so let's say class message and it'll take in two arguments the subject and the content and we'll just say we'll store these in instance variables subject is equal to subject and content is equal to content right okay um now by default if we make a new message so m equals message.new and then if we try to call m.content we should not be able to execute that method because content is this is an instance variable right we stored we stored the value for content in an instance variable but we haven't defined any readers so because we could make a new method called content that is a reader method for at content right and then this should execute just fine oh so we didn't initialize correctly subject my subject and then my content okay all right so we've got my content is now being printed out right we see that here my content is being printed out that's because we define this new reader method which accesses the instance variable so another alternative to that would be to say m.instance variable get and then pass in the value for the instance variable which actually requires the symbol there okay if we run this we see my content okay so this is another way that you can sort of get at the instance variable for content but what i wanted to show was that what we can do with with send is we can define some adder readers which is the same as we defined the method below earlier we can say subject and content here and then we can say you know you know subject content dot map do sim meaning the symbol for the name of the variable that we want to access and then we could say m dot send and pass in sim and so this should call each of those methods as it's mapping over so we'll say we'll store the result in some so this will be an array that contains the subject of the message and then it contains the content of the message so we could p result.join or you know puts result.join maybe like with a couple new lines and then print that out so we see my subject and we see my content so that's pretty cool but if you wanted to make a message that had you know dynamically so some variable number of um of possible fields in the message then you could get even even wilder where this this this array is defined somewhere even further up so we could say like you know fields is equal to subject content and then x right and then we can say add a reader for um splat of fields and this is going to take in now star args so we'll allow the the initializer to take in some variable number of arguments and then we can say you know fields dot map or fields that each do sim and then we can say like um self.send and we want to find the setter the setter method so in order to get the setter method we might pass in like the the symbol and then the equal sign so this is going to call the setter method and then we want to pass in maybe with index the the argument that was passed so args at i so as long as we're sort of following the the order here that works the other option would be to like take args as uh you know some dictionary and then key into it it's probably a little bit better but we're just gonna keep it simple so we're gonna call args.send or self.send so we're calling the setter method on ourselves with some value here now we don't actually have a setter method because we only have adder readers so we need to add our assessors for fields so let's see if this works okay so we get the same exact result as before but now our message object is sort of meta-programmed to take some variable number of fields if we were to pass in some actually let's let's also print we'll return um sim and then is and then the the value for the um the value that was stored so that we can see sort of how this is lining up so we see subject is my subject content is my content now let's let's change this from being coded hardcoded here to fields that we were mapping over the same thing that we're talking about above and you'll notice that x right now is nothing because we didn't pass in x when we were initializing message so we can do that here and say like this is x okay let me just clean that up a little bit okay so then if we run this again now we see you know subject is my subject content is my content x is this is x all right so that's kind of the output that we have at this point now what's super interesting is consider the case where we now have a method called send so if we were to define a method on message called send which like puts i'm sending the message then if we attempt to run this same code we're going to get a failure because here we're calling m.send and now send is actually defined on message so now we're seeing send wrong number of arguments given to expected 0. so here we're actually calling with the object and with the instance of the symbol but it's expecting zero arguments because we defined it here with zero arguments so uh it turns out that ruby if you've overridden send for some reason then you can use ruby's underscore underscore send underscore underscore method to achieve the same thing so let's run this and i am seeing what's going on here ah send so this one also needs the underscore underscore okay let's try this again all right so we're back to uh we're back to having the correct answer here so subject is my subject content is my content x is uh this is x take this all the way all the way to the finish line what i wanted to do is re-implement that inject method so that we can see how that might actually be used so before recall that we had this thing going on so we're calling inject we're passing in an initial value an initializer of zero and then the plus method i think if we leave off the zero let's actually so let's run this and we should get back 10 that is the sum of one two three four if we leave off the zero i believe we're we're still able to execute inject instead of using zero as the initial value for the accumulator instead i'll just use the first element in the array so let's let's try to implement our own method on array called my inject that will take in some initial value and then some symbol and then when when it's working through the objects it will sort of accumulate that and inject that and apply apply the method that we're passing here so if we run this right now nothing happens because my inject is not a method on the array class so in order to do that or to work with this we need to open the array class in monkey patch and add a method called mine jax will say class array def my inject and initially we'll just say like it's taking in some accumulator and then some symbol right okay so then what we need to do is we want to start off our result as the accumulator so we're going to say result equals accumulator and then we want to ultimately return our result at the bottom now in the middle here what we want to do is like loop over each element in the array and apply sim with the accumulator so we're going to do we can use the arrays underlying each method and we'll say that for each element what we want to do is we want to say that the result after after visiting each element in the array the result is equal to the element dot send sim for the result so this is how we're going to collect up the results so here the element the very first element is going to be one so we're going to say one dot send plus and we want to add 1 to the result which in the beginning is equal to the accumulator we passed in 0 as our accumulator so it's going to be 1 plus 0 equals 1 and we're going to store that in result then when we go to the next element 2 when we're visiting the next element we're going to say 2 dot send plus with result which was 1 from the previous loop so now we're going to see 1 plus 2 is 3. we're going to store that in result we're going to go visit 3. we'll say 3 plus plus the previous which was 3 equals 6 store then result and then finally when we add 4 we should get 10 back so if we run this we get back our result which is 10. but right now our my inject does not support taking in uh fewer arguments it doesn't support a default accumulator so what we could do is instead of taking acc and the sim we can take in star args and we can say if args.length is equal to 2 then let's see so if it's equal to 1 then we want the result to start off as like args zero otherwise we want the result to sorry if it's two we want it to start off as rx0 otherwise we want it to start off as self at zero and then we also i guess want to start off if we are using the first element in the array then we don't want to run the each loop over the entire thing so we kind of need to do this uh this thing here where we're saying like um if we have an accumulator we want to loop over all the elements um if we don't have an accumulator then we want to we want to loop over just the first first element it forward so this is this is super hacky super super hacky but we can say like self at one to the end dot each do that should work i believe all right so what's going on here sim is missing because yeah so we need to also pull out sim so that's going to be args one and then sim down here is going to be um args zero okay so then we get back 10 and it supports either the method where we give it an initial value so if we give it the initial value of 100 we should get 110 and it also supports just not not feeding it an initial value this is super duplicative and i'm sure we could um improve this by saying you know like what what do you start at um so we could just say like i equals zero here yeah let's do that and then we can say um you know otherwise i equals one and then we can just start from i and go to minus one or like the end of the list and we should get the same results here and we do okay so now let's let's change this even further so that it also supports the block style um so the other the other alternative is to pass in a block um so we could say yeah like my inject do um el acc and then we want to say like el plus acc is the the result um i think because of the way that puts works um i think we have to put parentheses around that my inject is nil my inject block in my inject nil is not a symbol or okay so um okay so if block given then we want to do something otherwise we want to do something else so in the case that there was no block given if if we got a symbol we want to we want to execute this otherwise we want to block we want to execute yeah let's let's move the block given um to here so if there was a block given then we will execute the block so we'll say result is equal to block.call and we'll pass in the element otherwise actually we need to we need to pass in both the element and the accumulator which is going to be result um okay so that should execute this block when we say block.call it's going to run this block and we'll run the block and this is the return value from the block and so we get back 10. so now our our my inject method supports all these different approaches so we can say yeah we can either take in just the symbol that we want to apply we can take in an accumulator in a symbol or we can take in a block so pretty cool stuff i think this might even work with an initial value so let's start our initial value at 100 and see if it works with a block style it does not why doesn't that work so my inject ah if the length is okay so checking the length is not enough we also have to check if um because that initial value that we passed in 100 that's making the length of the arguments to my inject to but it's using the block hmm yeah so that actually i actually don't know why that's not working p args.length ah because yeah because the block doesn't count as one of the arguments so um it seems like we're entering this block here so our checking the length of the arguments is not enough we would also need to check if elements in the array respond to but i'll cover respond in a in a different episode so i will share uh share the code for this in a gist and uh yeah until next time thanks for watching --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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