Listing an Object’s Methods in Ruby

What are Method objects?

A method in ruby is a named block of parameterized code connected with multiple objects. Many Languages compare functions and methods, but because ruby is a purely object-oriented language, all methods are true methods associated with at least one object. Methods are an important part of syntax in ruby, but they are not values that Ruby programs can operate on. 

Ruby has strong metaprogramming capabilities, and methods can be represented as instances of the Method class. Invoking a method through a Method Object is less efficient than invoking it directly. Method objects are not generally used as frequently as procs and lambdas. The Object class defines a method named "method." When we Pass it a method name as a string or a symbol, it returns a Method object representing the designated Method of the receiver. 

For example:

m = 0.method(:succ)  # A Method representing the succ method of Fixnum 0

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Problem 

Let's say we have given an unfamiliar object, and we want to see what methods are available to call.

Solution

All Ruby objects execute the object#methods method. It will return an array that contains the names of the object's public instance methods:

Object.methods 
# => ["name", "private_class_method", "object_id", "new", 
# "singleton_methods", "method_defined?", "equal?", … ]

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For getting a list of the singleton methods of some objects, we have to use the method known as Object1#singleton_methods:

Object1.singleton_methods    # => []
Fixnum1.singleton_methods    # => ["induced_from"] 
class NinjaClass
 def NinjaClass.my_singleton_method 
 end 
 def my_instance_method 
 end
end 
NinjaClass.singleton_methods    # => ["my_singleton_method"]

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Now, to list the instance methods of a class, we have to call instance_methods on the object. This allows us to list the instance methods of a class without instantiating the class:

''.methods == String.instance_methods         # => true

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The output of these methods can be more useful when they are sorted, therefore:

Object1.methods.sort

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Object1.methods.sortRuby also specifies some elementary predicates along the same lines. To look at whether a class defines a specific instance method, call method_defined? On the class or respond_to? On the instance class. And to also see call respond_to? On the instance class:

MyClass.method_defined? :my_instance_method   # => true  
MyClass.new.respond_to? :my_instance_method   # => true   
MyClass.respond_to? :my_instance_method       # => false  
MyClass.respond_to? :my_singleton_method      # => true 

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Discussion

When you are in an interactive session of ruby, we need to see what specific Method is called and which Method an object supports. If we are using a library like Facets and Rails or our code has been adding methods to the built-in classes, it is also considered reliable.

The below table is doing to discover protected, public, and private methods:

Just because we can see the names of protected and private methods in a table does not mean we can call the methods or respond_to? Will find them:

String.private_instance_methods.sort 
# => [:Array, :Complex, :Float, :Hash, :Integer, :Rational, :String, :__callee__, :__dir__, :__method__, :`, :abort, :at_exit, :autoload, :autoload?, :binding, :block_given?, :caller, :caller_locations, ...] 
String.new.respond_to? :autoload?               # => false 
String.new.autoload? 
# NoMethodError: private method 'autoload?' called for "":String

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Frequently Asked Questions

What are Methods in Ruby?

A method in ruby is a named block of parameterized code connected with multiple objects. Invoking a method through a Method Object is less efficient than invoking it directly. Method objects are not generally used as frequently as procs and lambdas.

What is Metaprogramming in ruby?

Metaprogramming in ruby is a technique by which you can write code that writes code by itself dynamically at runtime. In simple words, we can define methods and classes during runtime.

What is Ruby Method?

A method in Ruby is a set of expressions that returns a value. Within a method, you can set your code into subroutines that can be quickly initiated from other areas of their program.

What is the main object in Ruby?

In ruby, everything occurs in the context of some objects. The object at the highest level is called the "main." It is basically an instance of an object with the property that any methods defined in the main are added as the object's instance method.

Are variables objects in Ruby?

A variable in ruby is nothing but a label or tag for a container. A variable can contain almost everything like a string, an array, a hash, etc.

Conclusion

In this article, we have discussed reflection and meta-programming, and then we have seen how to list an object's Method in ruby with the help of an example. We started with the introduction of ruby, then we saw reflection and meta-programming concepts, and then the listing of an object's Method in ruby with the help of an example.

If you want to learn more about such topics, you can see  Introduction to ruby on rails, Directory Structure in Ruby, Ruby on Rails, and Ruby vs. Python. Also, refer to the Official Documentation and Ruby Koans. You can explore some more articles on For Loop in Ruby, Operators in Ruby, or directly access the Coding Ninjas Studio for our courses.

You can also refer to our guided path on Coding Ninjas Studio to upskill yourself in Data structure and algorithms, Competitive Programming, Javascript, and System Design. Do upvote our blogs if you find them helpful and engaging!

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