Module_eval for dynamic behavior in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does module_eval do in Ruby?

module_eval runs a string or block of code inside the context of a module or class, allowing you to add or change methods dynamically.

beginner

How can module_eval be used to add a method to a class?

<p>You pass a string defining the method to <code>module_eval</code>, and it adds that method to the class or module.</p><pre>MyClass.module_eval do
  def greet
    "Hello!"
  end
end</pre>

intermediate

What is a practical use case for module_eval?

It helps when you want to create methods or change behavior based on data or conditions at runtime, like generating methods from a list of names.

intermediate

What is the difference between module_eval and class_eval?

They are very similar; both evaluate code in the context of a module or class. class_eval is just an alias for module_eval when used on classes.

advanced

Can module_eval access instance variables of the module or class?

Yes, inside the block or string passed to module_eval, you can access and modify instance variables of the module or class.

What does module_eval primarily allow you to do?

A Compile Ruby code to machine code

B Create a new module

C Run code inside a module or class context

D Delete methods from a class

module_eval runs code inside the context of a module or class, enabling dynamic behavior.

Which of these is a correct way to add a method using module_eval?

A MyClass.module_eval { def hello; 'Hi'; end }

B MyClass.module_eval(:hello) { 'Hi' }

C MyClass.module_eval('hello')

D MyClass.module_eval(:def hello end)

Passing a block with method definition to module_eval adds the method.

What is a key benefit of using module_eval?

A Dynamic method creation at runtime

B Static code analysis

C Faster execution speed

D Memory optimization

module_eval allows creating or changing methods dynamically while the program runs.

Which is true about class_eval compared to module_eval?

A <code>class_eval</code> is only for classes, <code>module_eval</code> only for modules

B <code>class_eval</code> is an alias of <code>module_eval</code> for classes

C <code>class_eval</code> cannot add methods

D <code>module_eval</code> is deprecated

class_eval is just another name for module_eval when used on classes.

Can module_eval access instance variables of the module or class it is called on?

A Only if passed as arguments

B No, it only accesses class methods

C Only in Ruby versions before 2.0

D Yes, it can access and modify them

Inside module_eval, instance variables of the module or class are accessible.

Explain how module_eval can be used to add methods dynamically to a Ruby class.

Think about passing a block or string with method code.

Describe the difference and similarity between module_eval and class_eval.

Consider their usage on classes and modules.