Method objects with method() in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of calling a method object

What is the output of this Ruby code?

Ruby

class Greeter
  def hello
    "Hello, world!"
  end
end

g = Greeter.new
m = g.method(:hello)
puts m.call

A Hello, world!

B NoMethodError

C nil

D ArgumentError

💡 Hint

Remember that method(:name) returns a method object that you can call.

The method(:hello) returns a method object bound to g. Calling m.call runs hello and returns "Hello, world!".

🧠 Conceptual

intermediate

Understanding method objects and binding

Which statement about Ruby method objects created by method() is true?

A They automatically convert to procs when assigned to variables.

B They cannot be called more than once.

C They are bound to the object they were created from and remember its state.

D They are unbound and can be called on any object of the same class.

💡 Hint

Think about what happens when you call method(:name) on an object.

Method objects are bound to the specific object they come from, so they keep that object's state when called.

🔧 Debug

advanced

Identify the error when calling an unbound method

What error does this Ruby code produce?

Ruby

class Person
  def greet
    "Hi!"
  end
end

m = Person.instance_method(:greet)
m.call

A ArgumentError

B TypeError

C NameError

D UnboundMethodError

💡 Hint

Consider what instance_method returns and how it differs from method.

instance_method returns an unbound method that must be bound to an object before calling. Calling m.call without binding raises an ArgumentError because no receiver is given.

📝 Syntax

advanced

Correct way to convert a method object to a proc

Which option correctly converts a method object to a proc and calls it?

Ruby

class Calculator
  def double(x)
    x * 2
  end
end

calc = Calculator.new
m = calc.method(:double)
# call the method object as a proc with argument 5

A p = m.to_proc(5); puts p.call

B p = m.proc; puts p.call(5)

C p = m.to_proc; puts p.call

D p = m.to_proc; puts p.call(5)

💡 Hint

Check the correct method name to convert a method object to a proc and how to call it with arguments.

to_proc converts the method object to a proc. Then you can call it with arguments like p.call(5).

🚀 Application

expert

Using method objects to implement a callback system

You want to store multiple method objects from different instances and call them later. Which code snippet correctly stores and calls these method objects?

Ruby

class Worker
  def initialize(name)
    @name = name
  end
  def work
    "#{@name} is working"
  end
end

w1 = Worker.new("Alice")
w2 = Worker.new("Bob")
callbacks = []
# store method objects from w1 and w2
callbacks << w1.method(:work)
callbacks << w2.method(:work)

# call all stored callbacks and collect results
results = callbacks.map { |m| m.call }
puts results

A ["is working", "is working"]

B ["Alice is working", "Bob is working"]

C ["Alice", "Bob"]

D RuntimeError

💡 Hint

Think about how method objects keep their binding to the original instance.

Each method object remembers the instance it came from, so calling them later returns the correct string with the instance's name.