How Ruby interprets code at runtime - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

Ruby method call and variable scope

What is the output of this Ruby code when run?

Ruby

def greet
  name = "Alice"
  puts "Hello, #{name}!"
end

greet
puts name

A Hello, Alice!\nNameError: undefined local variable or method `name' for main:Object

B Hello, Alice!\nAlice

C NameError: undefined local variable or method `name' for main:Object\nHello, Alice!

D Hello, Alice!\nnil

💡 Hint

Think about where variables defined inside methods are accessible.

The variable name is local to the greet method. It is not accessible outside the method, so puts name raises a NameError.

❓ Predict Output

intermediate

Ruby block variable behavior

What will this Ruby code output?

Ruby

x = 10
[1, 2, 3].each do |x|
  puts x
end
puts x

A 1\n2\n3\n10

B 10\n10\n10\n10

C 1\n2\n3\n3

D 1\n2\n3\nNameError

💡 Hint

Consider if the block variable x affects the outer x.

The block variable x is a new variable local to the block and does not overwrite the outer x. So the last puts x prints 10.

🔧 Debug

advanced

Identify the runtime error in Ruby code

What error does this Ruby code raise when run?

Ruby

def divide(a, b)
  a / b
end

puts divide(10, 0)

A NoMethodError: undefined method `/`

B ArgumentError: wrong number of arguments

C TypeError: String can't be coerced into Integer

D ZeroDivisionError: divided by 0

💡 Hint

What happens when you divide by zero in Ruby?

Dividing by zero in Ruby raises a ZeroDivisionError.

🧠 Conceptual

advanced

Ruby constant lookup at runtime

Given this Ruby code, what will be printed when run?

Ruby

module A
  X = 100
  class B
    X = 200
    def self.show
      puts X
    end
  end
end

A::B.show

A NameError: uninitialized constant X

B 200

C 100

D nil

💡 Hint

Constants inside classes override outer module constants with the same name.

The constant X inside class B is 200, which is used by show. The outer A::X is not used here.

❓ Predict Output

expert

Ruby dynamic method definition and runtime behavior

What is the output of this Ruby code?

Ruby

class C
  define_method(:hello) do |name|
    "Hello, #{name}!"
  end
end

obj = C.new
puts obj.hello("Bob")

A ArgumentError: wrong number of arguments (given 1, expected 0)

B NoMethodError: undefined method `hello' for #<C:0x0000>

C Hello, Bob!

D SyntaxError: unexpected `do'

💡 Hint

Look at how define_method creates methods at runtime.

define_method dynamically defines an instance method hello that takes one argument and returns a greeting string.