Instance_variable_get and set in Ruby - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the value of the instance variable @name.

Ruby

class Person
  def initialize(name)
    @name = name
  end

  def get_name
    [1]
  end
end

person = Person.new("Alice")
puts person.get_name

Drag options to blanks, or click blank then click option'

A@name = name

Binstance_variable_set(:@name)

Cinstance_variable_get(:@name)

Dget_instance_variable(:@name)

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance_variable_set instead of instance_variable_get.

Trying to access @name directly inside another method without returning it.

The method instance_variable_get(:@name) returns the value of the instance variable @name.

2fill in blank

medium

Complete the code to set the value of the instance variable @age to 30.

Ruby

class Person
  def initialize(age)
    [1]
  end

  def get_age
    instance_variable_get(:@age)
  end
end

person = Person.new(30)
puts person.get_age

Drag options to blanks, or click blank then click option'

Ainstance_variable_get(:@age)

Binstance_variable_set(:@age, age)

C@age = age

Dset_instance_variable(:@age, age)

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance_variable_get instead of instance_variable_set.

Assigning @age directly without using the method.

The method instance_variable_set(:@age, age) sets the instance variable @age to the value of age.

3fill in blank

hard

Fix the error in the code to correctly set the instance variable @city to 'Paris'.

Ruby

class Location
  def initialize(city)
    [1]
  end

  def get_city
    instance_variable_get(:@city)
  end
end

loc = Location.new("Paris")
puts loc.get_city

Drag options to blanks, or click blank then click option'

Ainstance_variable_set(:@city, city)

Binstance_variable_get(:@city, city)

Cinstance_variable_set(:city, city)

D@city = city

Attempts:

3 left

💡 Hint

Common Mistakes

Missing '@' in the symbol for the variable name.

Using instance_variable_get instead of instance_variable_set.

The correct way to set the instance variable using instance_variable_set requires the variable name as a symbol with '@' and the value.

4fill in blank

hard

Fill both blanks to create a hash of instance variable names and their values for variables with names longer than 3 characters.

Ruby

class Data
  def initialize
    @id = 1
    @name = "Data"
    @val = 100
  end

  def long_vars
    vars = instance_variables.select { |var| var.to_s.[1] 3 }
    { var => instance_variable_get(var) [2] var in vars }
  end
end

data = Data.new
puts data.long_vars

Drag options to blanks, or click blank then click option'

Alength >

Blength <

Cfor

Dif

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for length comparison.

Using 'if' instead of 'for' in the hash comprehension.

The code selects instance variables with names longer than 3 characters using var.to_s.length > 3 and creates a hash using a for loop.

5fill in blank

hard

Fill all three blanks to set an instance variable dynamically, get its value, and print it.

Ruby

class DynamicVar
  def set_var(name, value)
    [1]
  end

  def get_var(name)
    [2]
  end
end

obj = DynamicVar.new
obj.set_var(:@color, "blue")
puts [3]

Drag options to blanks, or click blank then click option'

Ainstance_variable_set(name, value)

Binstance_variable_get(name)

Cobj.instance_variable_get(:@color)

Dobj.instance_variable_set(:@color, "blue")

Attempts:

3 left

💡 Hint

Common Mistakes

Using instance_variable_get to set a variable.

Trying to print the variable without calling instance_variable_get.

The method set_var uses instance_variable_set(name, value) to set the variable. The method get_var uses instance_variable_get(name) to get it. Finally, printing obj.instance_variable_get(:@color) shows the value.

Practice

1. What does the Ruby method instance_variable_get do?

easy

A. It reads the value of an instance variable by its name.

B. It deletes an instance variable from an object.

C. It creates a new instance variable with a given name.

D. It lists all instance variables of an object.

Solution

1. Step 1: Understand the method purpose

   instance_variable_get is used to access the value of an instance variable by passing its name as a symbol or string.

2. Step 2: Compare with other options

   It does not delete, create, or list variables; it only reads the value.

3. Final Answer:

   It reads the value of an instance variable by its name. -> Option A

4. Quick Check:

   instance_variable_get reads variable value [OK]

Hint: Remember: get = read value of variable [OK]

Common Mistakes:

• Confusing get with set (changing value)
• Thinking it deletes variables
• Assuming it lists all variables

2. Which of the following is the correct syntax to set an instance variable @name to "Alice" using instance_variable_set?

easy

A. object.instance_variable_set(:nam, "Alice")

B. object.instance_variable_set("nam", "Alice")

C. object.instance_variable_set(@name, "Alice")

D. object.instance_variable_set(:@name, "Alice")

Solution

1. Step 1: Understand the argument format

   The first argument to instance_variable_set must be the instance variable name as a symbol or string, including the '@' prefix.

2. Step 2: Check each option

   A: object.instance_variable_set(:nam, "Alice") misses '@'. B: object.instance_variable_set("nam", "Alice") misses '@'. C: passes a variable instead of symbol/string. D: uses :@name symbol correctly.

3. Final Answer:

   object.instance_variable_set(:@name, "Alice") -> Option D

4. Quick Check:

   Use symbol with '@' prefix for setting [OK]

Hint: Use symbol with '@' prefix to set variable [OK]

Common Mistakes:

• Omitting '@' in variable name
• Passing variable instead of symbol/string
• Using string without '@' prefix

3. What will be the output of this Ruby code?

class Person
  def initialize(name)
    @name = name
  end
end

p = Person.new("Bob")
puts p.instance_variable_get(:@name)

medium

A. Bob

B. nil

C. @name

D. Error

Solution

1. Step 1: Understand instance variable initialization

   The @name variable is set to "Bob" in the constructor.

2. Step 2: Use instance_variable_get to read value

   Calling instance_variable_get(:@name) returns the value "Bob" stored in @name.

3. Final Answer:

   Bob -> Option A

4. Quick Check:

   instance_variable_get returns stored value [OK]

Hint: instance_variable_get returns actual stored value [OK]

Common Mistakes:

• Expecting variable name instead of value
• Confusing with nil if variable not set
• Thinking it raises error if variable exists

4. Identify the issue in this Ruby code snippet:

class Car
  def initialize
    @speed = 0
  end

  def set_speed(value)
    instance_variable_set(:speed, value)
  end
end

car = Car.new
car.set_speed(50)
puts car.instance_variable_get(:@speed)

medium

A. The variable @speed is not initialized.

B. Cannot call instance_variable_set inside a method.

C. Missing '@' in instance_variable_set argument name.

D. instance_variable_get should use string, not symbol.

Solution

1. Step 1: Check instance_variable_set argument

   The argument to instance_variable_set must include '@' prefix to identify the instance variable.

2. Step 2: Identify the error

   Here, :speed is missing '@', so Ruby will not find the variable and will create a new one without '@', causing unexpected behavior.

3. Final Answer:

   Missing '@' in instance_variable_set argument name. -> Option C

4. Quick Check:

   Always include '@' in variable name for instance_variable_set [OK]

Hint: Always prefix variable name with '@' in set/get methods [OK]

Common Mistakes:

• Omitting '@' in variable name
• Thinking instance_variable_set can't be used in methods
• Confusing symbol and string usage

5. Given a class Box with private instance variable @content, how can you change its value to "Books" from outside the class using instance_variable_set?

hard

A. box.instance_variable_set(:conten, "Books")

B. box.instance_variable_set(:@content, "Books")

C. box.@content = "Books"

D. box.set_content("Books")

Solution

1. Step 1: Understand private variable access

   Private instance variables cannot be accessed or changed directly from outside the class using normal assignment.

2. Step 2: Use instance_variable_set with correct name

   Using instance_variable_set with the symbol including '@' allows changing the private variable from outside.

3. Step 3: Check options

   box.instance_variable_set(:@content, "Books") correctly uses :@content. box.instance_variable_set(:conten, "Books") misses '@', box.@content = "Books" is invalid syntax, box.set_content("Books") assumes a setter method which may not exist.

4. Final Answer:

   box.instance_variable_set(:@content, "Books") -> Option B

5. Quick Check:

   Use instance_variable_set with '@' to change private vars [OK]

Hint: Use '@' prefix symbol to set private variables externally [OK]

Common Mistakes:

• Omitting '@' in variable name
• Trying direct assignment to private variable
• Assuming setter method exists