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How do you know if a method is available to an object?

How do you know if a method is available to an object?

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Alexandre Calaça
·Feb 24, 2020·

4 min read

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Table of contents

  • Intro
  • Introduction to the solutions
  • 2 approaches
  • Summing up
  • Conclusion

Hey guys, how have you been? Hope you are healthy and happy.

Intro

Today, let's see how to check if a method is available to an object. Again, the goal of this article is to check if a specific method is available to an object.

Introduction to the solutions

In Ruby, there are often a bunch of different ways to get the same results. Sometimes, the chosen method or solution is just a matter of preference.

This is not common in other programming languages, that's why some newcomers might feel uncomfortable.

This article offers 2 possible approaches.

2 approaches

Basically, there are 2 approaches (methods):

  • class.methods
  • respond_to?

The first approach - The class.methods method

Syntax: parameter.class.methods Parameter: The value that it is going to be checked Method: class.methods Return: It returns all the methods available to the class

First things first, the class method alone allows us to see the class of the value. Let's see some examples:

irb(main):001:0> "alexandre-calaca".class
=> String
irb(main):002:0> 2014.class
=> Integer

Let's check one example with an integer object using the .class.methods approach:

irb(main):001:0> 2.class.methods
=> [:sqrt, :allocate, :superclass, :<=>, :<=, :>=, :==, :===, :autoload?, :autoload, :included_modules, :include?, :name, :ancestors, :attr, :attr_reader, :attr_writer, :attr_accessor, :instance_methods, :public_instance_methods, :protected_instance_methods, :private_instance_methods, :constants, :const_get, :const_set, :const_defined?, :class_variables, :remove_class_variable, :class_variable_get, :class_variable_set, :class_variable_defined?, :public_constant, :freeze, :inspect, :deprecate_constant, :private_constant, :const_missing, :singleton_class?, :prepend, :class_exec, :module_eval, :class_eval, :include, :<, :>, :remove_method, :undef_method, :alias_method, :protected_method_defined?, :module_exec, :method_defined?, :public_method_defined?, :to_s, :public_class_method, :public_instance_method, :define_method, :private_method_defined?, :private_class_method, :instance_method, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, :instance_variable_get, :instance_variables, :method, :public_method, :singleton_method, :define_singleton_method, :public_send, :extend, :to_enum, :enum_for, :pp, :=~, :!~, :eql?, :respond_to?, :object_id, :send, :display, :nil?, :hash, :class, :singleton_class, :clone, :dup, :itself, :yield_self, :taint, :tainted?, :untrust, :untaint, :trust, :untrusted?, :methods, :frozen?, :protected_methods, :singleton_methods, :public_methods, :private_methods, :!, :equal?, :instance_eval, :instance_exec, :!=, :__send__, :__id__]
irb(main):002:0>

Let's check one example with a string object:

irb(main):002:0> "alexandre".class.methods
=> [:try_convert, :new, :allocate, :superclass, :<=>, :<=, :>=, :==, :===, :autoload?, :autoload, :included_modules, :include?, :name, :ancestors, :attr, :attr_reader, :attr_writer, :attr_accessor, :instance_methods, :public_instance_methods, :protected_instance_methods, :private_instance_methods, :constants, :const_get, :const_set, :const_defined?, :class_variables, :remove_class_variable, :class_variable_get, :class_variable_set, :class_variable_defined?, :public_constant, :freeze, :inspect, :deprecate_constant, :private_constant, :const_missing, :singleton_class?, :prepend, :class_exec, :module_eval, :class_eval, :include, :<, :>, :remove_method, :undef_method, :alias_method, :protected_method_defined?, :module_exec, :method_defined?, :public_method_defined?, :to_s, :public_class_method, :public_instance_method, :define_method, :private_method_defined?, :private_class_method, :instance_method, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, :instance_variable_get, :instance_variables, :method, :public_method, :singleton_method, :define_singleton_method, :public_send, :extend, :to_enum, :enum_for, :pp, :=~, :!~, :eql?, :respond_to?, :object_id, :send, :display, :nil?, :hash, :class, :singleton_class, :clone, :dup, :itself, :yield_self, :taint, :tainted?, :untrust, :untaint, :trust, :untrusted?, :methods, :frozen?, :protected_methods, :singleton_methods, :public_methods, :private_methods, :!, :equal?, :instance_eval, :instance_exec, :!=, :__send__, :__id__]
Pros and cons of the first approach

As you can see, it's possible to see all the available methods to that specific object, it allows you to have a wide view of all the available methods, however, you might feel kinda stuck due to so many methods.

The second approach - The respond_to? method

Syntax: parameter.respond_to? ("method") Parameter: The value that it is going to be checked Method: The method's name Return: It returns a boolean value (true or false)

The respond_to? method allows us to identify if a certain object is able to take certain method and return true or false.

Let's check some examples with a true return:

irb(main):003:0> array = [1, 3, 5, 0]
irb(main):005:0> array.respond_to? ("push")
=> true
irb(main):006:0> (2.4).class
=> Float
irb(main):007:0> (2.4).respond_to? ("round")
=> true

Let's check some examples with a boolean return:

irb(main):008:0> "alexandre-calaca".class
=> String
irb(main):009:0> "alexandre-calaca".respond_to? ("sqrt")
=> false
irb(main):010:0> 2.class
=> Integer
irb(main):011:0> 2.respond_to? ("substring")
=> false
Pros and cons of the second approach

As you can see, it's really quick to check if the method is available to the object. The only downside is that it is only possible to check one method at at time.

Summing up

Together, the respond_to? and class.methods approaches let us know if a method is available to an object, which is something so important when we are developing or debugging.

Conclusion

In this article, it was possible to learn and practice how to know if a method is available to an object.

Hope it was useful.

That's for today. Let me know if you have any questions.

By the way, you help me a lot if you like and/or share this article.

 
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