Method objects with method() in Ruby - Mini Project: Build & Apply

Using Method Objects with method() in Ruby

📖 Scenario: You are building a simple calculator program that can reuse operations easily.

🎯 Goal: Learn how to create method objects using method() and call them later.

📋 What You'll Learn

Create a method named add that takes two numbers and returns their sum.

Create a method object from the add method using method(:add).

Call the method object with two numbers to get the sum.

Print the result of calling the method object.

💡 Why This Matters

🌍 Real World

Method objects let you treat methods like data. This helps when you want to reuse or pass around actions in your programs.

💼 Career

Understanding method objects is useful for Ruby developers working on flexible code, libraries, or frameworks that need to manipulate behavior dynamically.

1

Define the add method

Write a method named add that takes two parameters a and b and returns their sum.

Ruby

# Define the add method here
# Your code here

Hint

Use def add(a, b) to start the method and a + b to return the sum.

2

Create a method object from add

Create a variable called add_method and assign it the method object of add using method(:add).

Ruby

def add(a, b)
  a + b
end

# Create add_method as a method object from add
# Your code here

Hint

Use add_method = method(:add) to get the method object.

3

Call the method object with arguments

Call the method object add_method with arguments 5 and 7 and assign the result to a variable called result.

Ruby

def add(a, b)
  a + b
end

add_method = method(:add)

# Call add_method with 5 and 7 and store in result
# Your code here

Hint

Use result = add_method.call(5, 7) to call the method object.

4

Print the result

Print the value of the variable result using puts.

Ruby

def add(a, b)
  a + b
end

add_method = method(:add)

result = add_method.call(5, 7)

# Print the result
# Your code here

Hint

Use puts result to display the sum.

Practice

1. What does the Ruby expression obj.method(:foo) return?

easy

A. A Method object representing the method foo of obj

B. The result of calling foo on obj

C. A symbol :foo

D. An error because method is not a valid method

Solution

1. Step 1: Understand method usage

   The method method on an object returns a Method object representing the named method.

2. Step 2: Identify the return type

   Calling obj.method(:foo) returns a Method object, not the method's result or a symbol.

3. Final Answer:

   A Method object representing the method foo of obj -> Option A

4. Quick Check:

   obj.method(:foo) returns Method object [OK]

Hint: Remember: method returns a Method object, not the call result [OK]

Common Mistakes:

• Thinking it calls the method immediately
• Confusing with symbol :foo
• Assuming it returns a string or error

2. Which of the following is the correct syntax to get a Method object for the method greet on object person?

easy

A. person.send(:greet)

B. person.method[b greet]

C. person.method(greet)

D. person.method(:greet)

Solution

1. Step 1: Check argument type for method

   The method method expects a symbol representing the method name.

2. Step 2: Validate options

   person.method(:greet) uses a symbol :greet, which is correct. person.send(:greet) calls the method directly, returning its result instead of a Method object. person.method(greet) passes an undefined variable greet, causing error. person.method[b greet] uses brackets, which is invalid syntax.

3. Final Answer:

   person.method(:greet) -> Option D

4. Quick Check:

   Use symbol argument with method [OK]

Hint: Use a symbol like :greet inside method() [OK]

Common Mistakes:

• Confusing method() with send()
• Using brackets instead of parentheses
• Passing undefined variable instead of symbol

3. What is the output of the following Ruby code?

class Calculator
  def add(x, y)
    x + y
  end
end
calc = Calculator.new
adder = calc.method(:add)
puts adder.call(5, 7)

medium

A. 5 7

B. 12

C. add

D. NoMethodError

Solution

1. Step 1: Understand method object creation

   The method(:add) returns a Method object for add on calc.

2. Step 2: Calling the Method object

   Calling adder.call(5, 7) executes add(5, 7), which returns 12.

3. Final Answer:

   12 -> Option B

4. Quick Check:

   Method object call returns sum 12 [OK]

Hint: Use call on Method object to run method with arguments [OK]

Common Mistakes:

• Expecting method name or arguments printed
• Confusing output with error
• Not using call to invoke method

4. Identify the error in this Ruby code snippet:

class Person
  def name
    "Alice"
  end
end
p = Person.new
m = p.method(name)
m.call

medium

A. Missing quotes around method name in method(name)

B. Cannot call method on an object

C. Method name does not exist

D. Using call on Method object is invalid

Solution

1. Step 1: Check argument to method

   The argument name is used as a variable, but it should be a symbol or string representing the method name.

2. Step 2: Correct usage

   It should be p.method(:name) or p.method('name') to get the Method object.

3. Final Answer:

   Missing quotes around method name in method(name) -> Option A

4. Quick Check:

   Method name must be symbol or string [OK]

Hint: Always pass method name as symbol or string to method() [OK]

Common Mistakes:

• Passing bare method name without quotes or colon
• Thinking method is invalid on objects
• Confusing call usage

5. Given the following code, what will be the output?

class Greeter
  def initialize(name)
    @name = name
  end
  def greet
    "Hello, #{@name}!"
  end
end

g1 = Greeter.new("Bob")
g2 = Greeter.new("Sue")
m1 = g1.method(:greet)
m2 = g2.method(:greet)

puts m1.call
puts m2.call

hard

A. Hello, Sue!\nHello, Sue!

B. Hello, Bob!\nHello, Bob!

C. Hello, Bob!\nHello, Sue!

D. Error: undefined method greet

Solution

1. Step 1: Understand instance variables and method objects

   Each Greeter instance stores its own @name. The method(:greet) returns a Method object bound to that instance.

2. Step 2: Calling Method objects

   Calling m1.call runs greet on g1, printing "Hello, Bob!". Similarly, m2.call prints "Hello, Sue!".

3. Final Answer:

   Hello, Bob! Hello, Sue! -> Option C

4. Quick Check:

   Method objects keep instance context [OK]

Hint: Method objects remember their object, so output matches instance data [OK]

Common Mistakes:

• Assuming method objects lose instance context
• Expecting same output for both calls
• Confusing method object with class method