Block given? check in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does block_given? do in Ruby?

block_given? checks if a block was passed to the current method. It returns true if a block is present, otherwise false.

beginner

How do you use block_given? inside a method?

Inside a method, you call block_given? to test if a block was passed. If true, you can safely call yield to execute the block.

intermediate

What happens if you call yield without a block and don't check block_given??

Ruby raises a LocalJumpError because yield expects a block to be given. Using block_given? prevents this error by checking first.

beginner

Example: What will this method print?<br>

def greet
  if block_given?
    yield
  else
    puts 'Hello!'
  end
end

greet

This method prints Hello! because no block is given when calling greet. The block_given? check is false, so it runs the else part.

beginner

Why is block_given? useful in Ruby methods?

It lets methods behave differently depending on whether a block is passed. This makes methods flexible and safe by avoiding errors when no block is given.

What does block_given? return if a block is passed to the method?

A true

B false

C nil

D raises an error

block_given? returns true when a block is passed to the method.

What Ruby keyword is used to run the block inside a method?

A run

B call

C yield

D execute

yield runs the block passed to the method.

What error occurs if you use yield without a block and no block_given? check?

A LocalJumpError

B ArgumentError

C SyntaxError

D NoMethodError

Ruby raises LocalJumpError when yield is called without a block.

Which of these is a correct way to check if a block is given inside a method?

A if block_passed?

B if block_given?

C if has_block?

D if block?

block_given? is the correct Ruby method to check for a block.

What will this code print?<br>

def test
  if block_given?
    yield
  else
    puts 'No block'
  end
end

test { puts 'Block here' }

A No block

B Error

C Nothing

D Block here

The block is given, so yield runs it and prints 'Block here'.

Explain how block_given? helps avoid errors when using blocks in Ruby methods.

Think about what happens if you call yield without a block.

Describe a simple Ruby method that behaves differently when a block is given versus when it is not.

Use an example like greeting with or without a block.