Dynamically Creating Methods in Ruby

Defining Methods with class_eval and instance_eval

Additionally, there are instance eval and class eval, which can be used to create methods in ruby dynamically. These techniques enable the evaluation of any piece of code inside the context of a particular class or object. Using class_eval like this becomes liable to the slight overhead of parsing the code string. However, the benefit is that the methods we define need not use reflective APIs; they can query or set the value of an instance variable directly.

Let’s see an example of how class_eval and instance_eval can be used.

Foo = Class.new
  Foo.class_eval do
    def class_bar
      "This class_bar"
    end
  end
  Foo.instance_eval do
    def instance_bar
      "This instance_bar"
    end
  end
puts  Foo.new.class_bar   #=> "For class_bar"
puts   Foo.instance_bar       #=> "For instance_bar"

You can also try this code with Online Ruby Compiler

Run Code

The above code gives the following output:

Frequently Asked Questions

What is define_method Ruby?

You may utilize the define method_method in the Module class to dynamically generate methods. When using define_method, you use it with the name of the new method and a block, and the block's parameters become the new method's parameters.

What is metaprogramming in Ruby?

When using metaprogramming, code interacts with other code instead of data. It may be used to create programs that generate code as needed during execution. Ruby can open and change classes, make methods on the fly, and do much more thanks to metaprogramming.

What is method_missing in Ruby?

method_missing is a means to manage circumstances when you call a method that doesn't exist that Ruby gives you access to the inside of your objects. Like a Begin/Rescue for method calls, kind of. It provides one final opportunity for you to handle that method call before an exception is triggered.

Is Ruby dynamic typed?

Because Ruby is a dynamic language, types are verified as the code is executed. The compiler won't alert you if you attempt to call a method on an object that doesn't exist; instead, you'll learn about the issue when the code is run and receive a NoMethodError.

What is monkey patching in Ruby?

A Monkey Patch (MP) is a term used in Ruby to describe a dynamic alteration to a class, which may introduce new methods or replace existing ones. Ruby offers this capability to provide programmers additional freedom.

Conclusion

In this article, we have discussed Dynamically Creating Methods in ruby. We saw how we can use define_method and class_eval methods for dynamically creating methods in Ruby.

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• Introduction to Ruby
• Ruby from Coding Ninjas
• Everything you wished you knew about Ruby on Rails
• Ruby Official Documentation
• Ruby FAQ
• RubyKoans

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