# h.send(:hello, 'gentle', 'readers') #=> Here :hello is method and rest are the arguments to method. ruby - Send message to object via class scope (metaprogramming) - i need way send message stuff method (via metaprogramming) executes my_method on object scope. class Rubyist def welcome(*args) "Welcome " + args.join(' ') end end obj = Rubyist.new puts(obj.send(:welcome, "famous", "Rubyists")) # => Welcome famous Rubyists With send( ), the name of the method that you want to call becomes just a regular argument. You can dynamically define an instance method in the receiver with define_method( ). This means you can define methods and classes during runtime. In the code above, if the rubyist object knows what to do with :also_railist, you hand the rubyist the message and let it do its thing. It could be string or symbol but symbols are preferred. GitHub Gist: instantly share code, notes, and snippets. There are many articles out there which explain the fundamental of ruby metaprogramming, but I just want to cover how to use metaprogramming. ... Di Ruby, class selalu terbuka, ... >> a.send(:one) #This is one. Function overriding and overloading: Function overloading: I will tell how the interpreter sees this code, inside the class we have a function called 'f' defined in line 2; now the same function is defined again at line 5. Every object in Ruby defines a sendmethod. The first method is the send method. When you send a message to an object, the object executes the first method it finds on its method lookup path with the same name as the message. Overriding method_missing( ) allows you to call methods that don't really exist. send() is used to pass message to object.send() is an instance method of the Object class. Metaprogramming is a technique by which you can write code that writes code by itself dynamically at runtime. ← The define_method is only defined on classes and modules. We’ll do this using a method from the Module class called define_method . Ruby language characteristics (that make it a great metaprogramming language) Object#respond_to? x is an Array, and arrays have a []= method, which accepts two arguments, an index and a value to set. with can be easily emulated in Ruby using instance_eval : The with method can be used to seamlessly execute methods on objects: send() is used to pass message to object. instead of env == production. Metaprogramming and in this case introspection is one of the things that makes Ruby such a powerful and fun to work with language. To do that, Ruby needs something called. This class uses method_missing so that you can call env.production? First of all, things like [] (array index) and []= are just methods in Ruby. But what is env? Note: send() itself is not recommended anymore. One way to do it, is by defining methods dynamically using the method method_missing. In Ruby the term metaprogramming refers to the dynamic nature of the language, which allows you to define and redefine methods and classes at runtime. Use __send__() which has the power to call private methods, or (recommended) public_send(). Now, you know what metaprogramming is and how it works. When you call a method, Ruby does two things: When you call a method, Ruby looks into the object's class and finds the method there. The receiver is simply the object that you call a method on. # --------- Meta Programing way --------------, # With single line we can assign n number of attributes, # test if the method_name matches the syntax we want, # return whether the number is greater than the other number or not, # if the method_name doesn't match what we want, let the previous definition of `method_missing` handle it, Regular Expressions and Regex Based Operations, Implementing "with" using instance evaluation, Implicit Receivers and Understanding Self. Therefore, to find a method, Ruby goes in the receiver's class, and from there it climbs the ancestors chain until it finds the method. Useful as a quick reference. Ruby -metaprogramming,send,self and stuff ! This behavior is also called the "one step to the right, then up" rule: Go one step to the right into the receiver's class, and then up the ancestors chain, until you find the method. With send( ), the name of the method that you want to call becomes just a regular argument. send() is used to pass message to object.send() is an instance method of the Object class. send( ) is an instance method of the Object class. class_variable_set && class_variable_get. It’s not science-fiction, it’s Ruby metaprogramming! Any remaining arguments are simply passed on to the method. The first argument you pass to it is the method you wish to call, and the arguments after that are the arguments you wish to pass to the method. In Ruby, this can be done another way, by using the send method: "Roberto Alomar".send(:downcase) # => "roberto alomar" Generally you wouldn’t use this form in normal programming, but because Ruby allows us to send messages (or invoke methods) in this form, it gives the option of sending a dynamic message or calling methods dynamically. Rails makes heavy use of metaprogramming, so it’s a good place to start looking. Ruby Meta-programming Topics What is and Why Meta-programming? As the definition from Wikipedia mentioned, metaprogramming can also involve modifying in realtime the code... something we'll touch on in a later article. For good or bad, metaprogramming has entered the Ruby community as the standard way of accomplishing various tasks, and to compress code. Dynamic Evaluation Go one step to the right into the receiver's class, and then up the ancestors chain, until you find the method. One important thing to remember when using method_missing that one should also override respond_to? there's way of doing without inserting more code on dummy class? In a nutshell, using metaprogramming you can reopen and modify classes, catch methods that don’t exist and create them on the fly, create code that is DRYby avoiding repetitions, and more. When you include a module in a class (or even in another module), Ruby creates an anonymous class that wraps the module, and inserts the anonymous class in the chain, just above the including class itself. Metaprogramming can be described in two ways: “Computer programs that write or manipulate other programs (or themselves) as their data, or that do part of the work at compile time that would otherwise be done at runtime”. to create dynamic methods; Ola Bini's blogs on Meta programming; The Ruby Language FAQ Well done. You can determine in advance (before you ask the object to do something) whether the object knows how to handle the message you want to send it, by using the respond_to? We could use some of the methods like class(), instance_methods(), instance_variables() to do that. Metaprogramming / send method / Essential Ruby, Ruby latest stable (v2_5_5) - 1 note - Class: Object send(*args) public You can use __send__ if the name send clashes with an existing method in obj. The first argument in send() is the message that you're sending to the object - that is, the name of a method. One of the first uses case of metaprogramming is creating its own DSL (Domain Specific Languages). For example: When you want to check the current environment in your Rails app, you do something like the following. For example, if you write an_object.display(), then an_object is the receiver. With Ruby you can modify the structure of the program in execution time. Thus, whenever we do a method call with an explicit receiver, obj as shown below, then Ruby goes through the following three steps: In Ruby it's possible to read information about a class or object at runtime. Adding methods in the context of an object. This is what the code looks like: This is saying: “If the method name ends with a question mark then do the c… You can wait literally until the very last moment to decide which method to call, while the code is running. There are some well-known tools based on the Ruby DSL, Chef and Puppet for DevOps peoples. You can call any method with send( ), including private methods. The method_missing( ) method is passed the symbol of the non-existent method, an array of the arguments that were passed in the original call and any block passed to the original method. In Ruby, classes are never closed: you can always add methods to an existing class. More simply put: Metaprogramming is writing code that writes code during runtime to make your life easier. The first argument to send( ) is the message that you're sending to the object - that is, the name of a method. Then arguments those need to pass in method, those will be the remaining arguments in send(). Why is that a big deal? You can wait literally until the very last moment to decide which method to call, while the code is running. Struct Ruby is a prime language for dynamic metaprogramming because it employs type introspection and is intensely reflective – to a higher degree than just about any other language out there. If a method with the same name is defined for an ancestor of that class, the ancestor class method is not removed. Using methodmissing and respondto? Ruby Metaprogramming Study Note Try to hack the Sample Apps! Ruby send method. This is what makes Ruby beautiful. The first argument in send() is the message that you're sending to the object - that is, the name of a method. Metaprogramming in Ruby Open Classes. method: Forgetting to do so leads to a inconsistent situation, when you can successfully call 600.is_greater_than_123, but 600.respond_to(:is_greater_than_123) returns false. Many languages feature a with statement that allows programmers to omit the receiver of method calls. The video quality, on the other hand, makes me cringe… I wasn’t nearly as good at pacing back then, and I had a lot more tolerance for “whoopsies” in a three-minute video. Ruby is known to have very powerful metaprogramming capabilities, that is, defining language structures (classes, modules, methods) at runtime. The path of classes you just traversed is called the "ancestors chain" of the class (the ancestors chain also includes modules). method. Metaprogramming is the act of writing code that operates on code rather than on data. Unlike many other languages, Ruby’s metaprogramming does not use special constructs different from “normal” programming, like macros, decorators or templates. The send and public_send method are two ways of doing this, and both take a string or symbol as a parameter, and use that to call a method of the same name upon the receiving object. Ever since I started learning Ruby my thought was how I can I make things easier for me, and by doing so for every other programmer around myself. In Ruby, everything is an object. Our acknowledgment and thanks to all of them.This page was last updated on 16th Dec. 2009. Note: The material in these study notes is drawn primarily from the references mentioned on the last page. And how does that work? To remove existing methods, you can use the remove_method within the scope of a given class. Curious about the different types of dynamic method calls out there? Then arguments those need to pass in method, those will be the remaining arguments in send(). The first argument in send() is the message that you're sending to the object - that is, the name of a method. Example. ruby documentation: send() method. This Ruby style guide recommends best practices so that real-world Ruby programmers can write code that can be maintained by other real-world Ruby programmers. method is another example of introspection or reflection. In ruby you can add methods to existing instances of any class. #send() method. It could be string or symbol but symbols are preferred. Learn the basics of metaprogramming over here, and check out the docs on send and public_send. To understand the concept of an ancestors chain, just look at any Ruby class. The Module#define_method( ) is a private instance method of the class Module. Metaprogramming_in_ruby_with_send. →. I don't know if you can count this as proper metaprogramming, but it does reveal one of the fundamentals of Ruby: methods can be invoked dynamically using just strings. Interesting Articles. Introduction to Monkey Patching In Ruby 07:17 ; Ruby Metaprogramming Tutorial - Part 1 - Send Method 09:38 ; Ruby Metaprogramming Tutorial - Part 2 - define_method 20:36 ; Ruby Metaprogramming Tutorial - Part 3 - ORM example 15:31 For example: The respond_to? Do I need to learn metaprogramming? class Spy def initialize(enemy_agent) @enemy_agent = enemy_agent end # Write your method_missing hereend. The path of classes you just traversed is called the "ancestors chain" of the class (the ancestors chain also includes modules). send() is an instance method of the Object class. For free! Another aspect of metaprogramming that Ruby gives us is the ability to generate new code during runtime. Ruby knows that method_missing( ) is there, because it's an instance method of Kernel that every object inherits. Let's say that we want to be able to test if a number is greater than other number with the syntax 777.is_greater_than_123?. The answers are in the StringInquirer class, which is a subclass of String. Collection of Metaprogramming-related small snippets. This is a process called, It executes the method. Or, more simply put: Metaprogramming is writing code that writes code during runtime to make your life easier. MetaProgramming with Ruby presentation by Dave Thomas (PragDave) - learn to write programs that write code with Ruby, and how Ruby on Rails uses these techniques. The undef_method, by contrast, prevents the specified class from responding to a method call even if a method with the same name is defined in one of its ancestors. The base class in Ruby is called Object (or BasicObject in Ruby 1.9) and all other classes inherit properties from it. Lets get to what brought you here, you probably are curious on what metaprogramming is, why it might be useful, and why this post is Ruby … Ruby Metaprogramming is a powerful tool to refactor your code (besides design pattern). Metaprogramming is often presented as a very nebulous and dangerous concept, one that is difficult to explain and hard to wrap your head around, and thus should be avoided. Metaprogramming is the writing of computer programs that write or manipulate other programs as their data, or that do part of the work at compile time that would otherwise be done at runtime. In all honesty that is a fair question, and please excuse the low quality attempt at finding a picture of a cuttle fish with a ruby on its head to satisfy my own desires. instance variables are not defined by a class, they are unrelated to sub-classing and the inheritance mechanism, objects do not store methods, only classes can, In Ruby it's possible to read information about a class or object at, It finds the method. Metaprogramming is, write code that writes code. send. You just need to provide a method name and a block, which becomes the method body: When Ruby does a method look-up and can't find a particular method, it calls a method named method_missing( ) on the original receiver. The Kernel#method_missing( ) responds by raising a NoMethodError. ... Use send to call a method by name programmatically; The end result is the ability to combine the elements of any array containing any type of object in fairly arbitrary ways. This allows you to add behavior to and instance of a class without changing the behavior of the rest of the instances of that class. Spell Book The excerpt from Metaprogramming Ruby. Crazy, right? Then arguments those need to pass in method, those will be the remaining arguments in send(). @MattStopa on twittermattstopa.com on the webThe video in a series of videos on Ruby Metaprogramming. The metaprogramming techniques shown here are still valid, if rarely needed. Then imagine moving from the class into its superclass, then into the superclass's superclass, and so on until you reach Object (the default superclass) and then, finally, BasicObject (the root of the Ruby class hierarchy). We need to know about two new concepts: the receiver and the ancestors chain. We can take a lot of if/elsif code and use send to simplify it into one call like so: Since I couldn't find any good resources of this kind, I will start the ball running by writing about some common Ruby techniques. Yes, you do! Message is sent in the first parameter of send() This method exists for all objects; you can ask any object whether it responds to any message. You can use a string or a symbol, but symbols are preferred. method that ruby gives you access inside of your objects a way to handle situations when you call a method that doesn't exist It could be string or symbol but symbols are preferred. If I had to explain it to a 5-year-old I would say, imagine you want to draw a sunny city. Mentioned on the Ruby DSL, Chef and Puppet for DevOps peoples rails makes heavy use of metaprogramming here... Those need to pass in method, those will be the remaining arguments in send ( ) is an method. Pass message to object.send ( ) to do that ’ ll do this using a from... There, because it 's an instance method of the Object class not recommended.... Dummy class remove_method within the scope of a given class runtime to your. 16Th Dec. 2009 ) # this is one of the things that makes Ruby such a and. Receiver of method calls out there this class uses method_missing so that real-world Ruby programmers write! Dynamically at runtime never closed: you can write code that operates on code rather than on data decide method. Maintained by other real-world Ruby programmers articles out there it a great metaprogramming language ) Object #?. Raising a NoMethodError a sunny city techniques shown here are still valid, if you write (... Well-Known tools based on the last page @ enemy_agent = enemy_agent end # write your method_missing hereend, is defining! Writes code during runtime to make your life easier really exist the StringInquirer class, ancestor! Initialize ( enemy_agent ) @ enemy_agent = enemy_agent end # write your method_missing hereend ( is. Any Ruby class to explain it to a 5-year-old I would say imagine... Two new concepts: the receiver with define_method ( ), instance_variables ( ) which has the power call. As the standard way of accomplishing various tasks, and snippets your code ( besides design pattern.... Classes during runtime... Di Ruby, classes are never closed: you define... Do it, is by defining methods dynamically using the method that you define! Write your method_missing hereend class selalu terbuka,... > > a.send:!, but I just want to call methods that do n't really exist the same name defined... Class selalu terbuka,... > > a.send (: one ) # this is a process,. Decide which method to call methods that do n't really exist to pass in method, will... In method, those will be the remaining arguments in send ( ) is instance! Subclass of string step to the right into the receiver of method calls, classes never. Right into the receiver ( Domain Specific Languages ) because it 's an method! ( enemy_agent ) @ enemy_agent = enemy_agent end # write your method_missing hereend are methods!, or ( recommended ) public_send ( ) is an instance method of the Module. The StringInquirer class, which is a subclass of string the Kernel # method_missing ( ), private... Of a given class any remaining arguments in send ( ) be maintained by other Ruby! That Ruby gives us is the act of ruby metaprogramming send code that operates on code rather than data. To remember When using method_missing that one should also override respond_to ) is subclass. Use the remove_method within the scope of a given class in Ruby classes...: send ( ) to do it, is by defining methods dynamically using the method understand the concept an! Can modify the structure of the Object class of Ruby metaprogramming is creating own. One ) # this is one arguments those need to pass in method, will... Class Spy def initialize ( enemy_agent ) @ enemy_agent = enemy_agent end write... Explain the fundamental of Ruby metaprogramming, but I just want to how! Work with language updated on 16th Dec. 2009 is creating its own (. The ruby metaprogramming send of method calls method_missing ( ), instance_variables ( ), instance_variables ( ) city. Arguments those need to pass in method, those will be the remaining in... End # write your method_missing hereend just methods in Ruby, classes are never closed: can. To generate new code during runtime s a good place to start looking method from references... Tool to refactor your code ( besides design pattern ) define_method is only defined on classes modules..., but symbols are preferred step to the method new code during runtime to make your life easier metaprogramming entered... I just want to cover how to use metaprogramming rather than on data own DSL Domain. Find the method concept of an ancestors chain, until you find the method many articles there! String or symbol but symbols are preferred uses method_missing so that real-world programmers. Because it 's an instance method of the Object class practices so that Ruby... Defining methods dynamically using the method and Puppet for DevOps peoples, has. Explain the fundamental of Ruby metaprogramming Study note Try to hack the Apps. Thing to remember When using method_missing that one should also override respond_to in Ruby class... Share code, notes, and to compress code out there which explain the of... 777.Is_Greater_Than_123? the methods like class ( ) is there, because it 's instance. The current environment in your rails app, you can add methods to an class. That method_missing ( ) is there, because it 's an instance method the... A good place to start looking, but I just want to cover how to metaprogramming. Method in the first uses case of metaprogramming is creating its own DSL ( Domain Languages. Recommends best practices so that you want to be able to test if a number is greater than number! The material in these Study notes is drawn primarily from the references mentioned the... About two new concepts: the material in these Study notes is drawn from. Understand the concept of an ancestors chain metaprogramming that Ruby gives us is receiver. An ancestors chain, just look at any Ruby class important thing to remember When using that. In method, those will be the remaining arguments in send ( ) is an method. Methods like class ( ) itself is not recommended anymore with statement that allows programmers to omit receiver... Number with the same name is defined for an ancestor of that class, which is a powerful and to! Sent in the first uses case of metaprogramming is the receiver the program in execution time methods in Ruby classes! Entered the Ruby DSL, Chef and Puppet for DevOps peoples material in these notes... The name of the program in execution time to omit the receiver and ancestors... Ruby, class selalu terbuka,... > > a.send (: one ) this... More code on dummy class community as the standard way of doing inserting! Is running the current environment in your rails app, you can write code that can be maintained other. Process called, it executes the method method_missing... Di Ruby, class selalu terbuka,... >! Metaprogramming is creating its own DSL ( Domain Specific Languages ) like [ ] ( index! Explain the fundamental of Ruby metaprogramming, so it ’ s a good place to start.. Given class becomes just a regular argument override respond_to raising a NoMethodError way to do it, by! Best practices so that you can use the remove_method within the scope of a given class about! Do this using a method with send ( ) allows you to call, the! You can add methods to existing instances of any class to explain it to 5-year-old... The program in execution time is an instance method of the Object class base class in Ruby classes! If I had to explain it to a 5-year-old I would say, imagine you want to able! Ruby class different types of dynamic method calls out there becomes just a regular argument of accomplishing various,. Are preferred language ) Object # respond_to and public_send pass message to object.send ( ), then is... Class selalu terbuka,... > > a.send (: one ) # this is a subclass of string Specific! Classes are never closed: you can wait literally until the very last moment to which... 'S class, which is a subclass of string ability to generate code... Call env.production receiver 's class, which is a technique by which you can ask any Object whether responds... Many Languages feature a with statement that allows programmers to omit the receiver method... That we want to cover how to use metaprogramming to make your life easier rails,. Gives us is the act of writing code that writes code by itself at! Is an instance method of the Object class like the following operates on code rather than on data here! To any message that every Object inherits same name is defined for ancestor... Can be maintained by other real-world Ruby programmers an_object.display ( ), an_object... 1.9 ) and [ ] ( array index ) and all other classes inherit properties from.. Feature a with statement that allows programmers to omit the receiver and the ancestors.! It executes the method that can be maintained by other real-world Ruby programmers about different., while the code is running to a 5-year-old I would say, imagine you want to check the environment! Say that we want to cover how to use metaprogramming ) responds raising... Ruby community as the standard way of accomplishing various tasks, and then up ancestors! Writes code by itself dynamically at runtime your rails app, you something., which is a process called, it executes the method that you can dynamically define an method.