Define_method with closures in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does define_method do in Ruby?

define_method creates a new method dynamically with a given name and block of code.

beginner

What is a closure in Ruby?

A closure is a block, proc, or lambda that remembers the variables from the place where it was defined, even if called elsewhere.

intermediate

How does define_method use closures?

The block passed to define_method acts as a closure, capturing variables from the surrounding scope to use inside the new method.

intermediate

Example: What will this code output?<br><pre>class Greeter
  def initialize(name)
    @name = name
    self.class.define_method(:greet) do
      "Hello, #{@name}!"
    end
  end
end

g = Greeter.new("Alice")
puts g.greet</pre>

The output will be Hello, Alice! because the block captures @name from the instance.

intermediate

Why is it useful that define_method blocks are closures?

It lets the dynamically created method access variables from where it was defined, allowing flexible and powerful method creation.

What does the block passed to define_method capture?

A Variables from the surrounding scope (closure)

B Only global variables

C Nothing, it has no access to outside variables

D Only method arguments

The block acts as a closure, capturing variables from where it was defined.

Which keyword is used to create a method dynamically in Ruby?

A def_method

B define_method

C create_method

D method_define

define_method is the correct Ruby method to define methods dynamically.

If a variable is defined outside define_method block, can the method access it?

A Yes, because the block is a closure

B No, it can only access its own variables

C Only if the variable is global

D Only if passed as an argument

The block remembers variables from its defining scope, so it can access them.

What will happen if you call define_method inside an instance method?

A It causes a syntax error

B It defines a method only for that instance

C It defines a global method

D It defines a method on the class using the closure of the instance method

The method is defined on the class, but the block can capture instance variables from the instance method.

Why might you use define_method with closures?

A To avoid using instance variables

B To speed up method calls

C To create methods that remember specific data from when they were defined

D To create global variables

Closures let the method remember data from its creation context, making it flexible.

Explain how define_method uses closures to access variables from its defining scope.

Think about how blocks remember variables around them.

Describe a simple example where define_method with a closure can be useful in Ruby.

Imagine creating personalized greeting methods.