First of all, things like [] (array index) and []= are just methods in Ruby. With Ruby you can modify the structure of the program in execution time. Go one step to the right into the receiver's class, and then up the ancestors chain, until you find the method. Ruby Metaprogramming Study Note Try to hack the Sample Apps! 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. GitHub Gist: instantly share code, notes, and snippets. For example: The respond_to? For good or bad, metaprogramming has entered the Ruby community as the standard way of accomplishing various tasks, and to compress code. 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. 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. The first argument in send() is the message that you're sending to the object - that is, the name of a method. class_variable_set && class_variable_get. ... Di Ruby, class selalu terbuka, ... >> a.send(:one) #This is one. Ruby Metaprogramming is a powerful tool to refactor your code (besides design pattern). Ruby knows that method_missing( ) is there, because it's an instance method of Kernel that every object inherits. method is another example of introspection or reflection. →. Why is that a big deal? The path of classes you just traversed is called the "ancestors chain" of the class (the ancestors chain also includes modules). This means you can define methods and classes during runtime. This method exists for all objects; you can ask any object whether it responds to any message. send( ) is an instance method of the Object class. Then arguments those need to pass in method, those will be the remaining arguments in send(). 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 is, write code that writes code. If a method with the same name is defined for an ancestor of that class, the ancestor class method is not removed. # --------- 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. send. Example. To do that, Ruby needs something called. Note: The material in these study notes is drawn primarily from the references mentioned on the last page. Ruby -metaprogramming,send,self and stuff ! Useful as a quick reference. We could use some of the methods like class(), instance_methods(), instance_variables() to do that. there's way of doing without inserting more code on dummy class? Use __send__() which has the power to call private methods, or (recommended) public_send(). 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. ... 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. Collection of Metaprogramming-related small snippets. 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. 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? Any remaining arguments are simply passed on to the method. The first argument in send() is the message that you're sending to the object - that is, the name of a method. It could be string or symbol but symbols are preferred. Yes, you do! 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. Metaprogramming and in this case introspection is one of the things that makes Ruby such a powerful and fun to work with language. It could be string or symbol but symbols are preferred. 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. This is a process called, It executes the method. 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 the term metaprogramming refers to the dynamic nature of the language, which allows you to define and redefine methods and classes at runtime. Learn the basics of metaprogramming over here, and check out the docs on send and public_send. 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. You can dynamically define an instance method in the receiver with define_method( ). One of the first uses case of metaprogramming is creating its own DSL (Domain Specific Languages). Since I couldn't find any good resources of this kind, I will start the ball running by writing about some common Ruby techniques. method that ruby gives you access inside of your objects a way to handle situations when you call a method that doesn't exist For free! send() is used to pass message to object.send() is an instance method of the Object class. Metaprogramming_in_ruby_with_send. In ruby you can add methods to existing instances of any class. Then arguments those need to pass in method, those will be the remaining arguments in send(). And how does that work? 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. Interesting Articles. Unlike many other languages, Ruby’s metaprogramming does not use special constructs different from “normal” programming, like macros, decorators or templates. You can call any method with send( ), including private methods. 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. We can take a lot of if/elsif code and use send to simplify it into one call like so: Or, more simply put: Metaprogramming is writing code that writes code during runtime to make your life easier. ruby - Send message to object via class scope (metaprogramming) - i need way send message stuff method (via metaprogramming) executes my_method on object scope. send() is used to pass message to object.send() is an instance method of the Object class. Ruby is known to have very powerful metaprogramming capabilities, that is, defining language structures (classes, modules, methods) at runtime. Metaprogramming is the act of writing code that operates on code rather than on data. 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. Ruby Meta-programming Topics What is and Why Meta-programming? Spell Book The excerpt from Metaprogramming Ruby. Ruby send method. Metaprogramming in Ruby Open Classes. ← 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. @MattStopa on twittermattstopa.com on the webThe video in a series of videos on Ruby Metaprogramming. #send() method. For example: When you want to check the current environment in your Rails app, you do something like the following. Message is sent in the first parameter of send() The Kernel#method_missing( ) responds by raising a NoMethodError. The first argument in send() is the message that you're sending to the object - that is, the name of a method. Now, you know what metaprogramming is and how it works. Using methodmissing and respondto? ruby documentation: send() method. class Spy def initialize(enemy_agent) @enemy_agent = enemy_agent end # Write your method_missing hereend. Many languages feature a with statement that allows programmers to omit the receiver of method calls. One way to do it, is by defining methods dynamically using the method method_missing. 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. 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. You can wait literally until the very last moment to decide which method to call, while the code is running. This class uses method_missing so that you can call env.production? 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. send() is an instance method of the Object class. Our acknowledgment and thanks to all of them.This page was last updated on 16th Dec. 2009. # h.send(:hello, 'gentle', 'readers') #=> Here :hello is method and rest are the arguments to method. Struct The path of classes you just traversed is called the "ancestors chain" of the class (the ancestors chain also includes modules). 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 to create dynamic methods; Ola Bini's blogs on Meta programming; The Ruby Language FAQ The define_method is only defined on classes and modules. The base class in Ruby is called Object (or BasicObject in Ruby 1.9) and all other classes inherit properties from it. 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. Overriding method_missing( ) allows you to call methods that don't really exist. But what is env? 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. Every object in Ruby defines a sendmethod. x is an Array, and arrays have a []= method, which accepts two arguments, an index and a value to set. There are some well-known tools based on the Ruby DSL, Chef and Puppet for DevOps peoples. Well done. This is what makes Ruby beautiful. Adding methods in the context of an object. 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. In Ruby, everything is an object. You can use a string or a symbol, but symbols are preferred. 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. Curious about the different types of dynamic method calls out there? To understand the concept of an ancestors chain, just look at any Ruby class. The answers are in the StringInquirer class, which is a subclass of String. One important thing to remember when using method_missing that one should also override respond_to? As the definition from Wikipedia mentioned, metaprogramming can also involve modifying in realtime the code... something we'll touch on in a later article. 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. Then arguments those need to pass in method, those will be the remaining arguments in send(). 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. This is what the code looks like: This is saying: “If the method name ends with a question mark then do the c… It’s not science-fiction, it’s Ruby metaprogramming! In Ruby, classes are never closed: you can always add methods to an existing class. 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. You can wait literally until the very last moment to decide which method to call, while the code is running. 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. Another aspect of metaprogramming that Ruby gives us is the ability to generate new code during runtime. If I had to explain it to a 5-year-old I would say, imagine you want to draw a sunny city. For example, if you write an_object.display(), then an_object is the receiver. The first argument to send( ) is the message that you're sending to the object - that is, the name of a method. There are many articles out there which explain the fundamental of ruby metaprogramming, but I just want to cover how to use metaprogramming. Metaprogramming is a technique by which you can write code that writes code by itself dynamically at runtime. 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. Note: send() itself is not recommended anymore. With send( ), the name of the method that you want to call becomes just a regular argument. Ruby language characteristics (that make it a great metaprogramming language) Object#respond_to? 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. 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 … Dynamic Evaluation Rails makes heavy use of metaprogramming, so it’s a good place to start looking. instead of env == production. The Module#define_method( ) is a private instance method of the class Module. Crazy, right? The metaprogramming techniques shown here are still valid, if rarely needed. It could be string or symbol but symbols are preferred. Do I need to learn metaprogramming? More simply put: Metaprogramming is writing code that writes code during runtime to make your life easier. method. To remove existing methods, you can use the remove_method within the scope of a given class. We’ll do this using a method from the Module class called define_method . The receiver is simply the object that you call a method on. 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 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. The first method is the send method. 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. 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