Yield to execute blocks in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the yield keyword do in Ruby?

yield pauses the method and runs the block of code given to the method, then returns to the method.

beginner

How do you pass a block to a method in Ruby?

You write the method call with a block using { ... } or do ... end after the method name.

intermediate

What happens if a method calls yield but no block is given?

Ruby raises a LocalJumpError because it expects a block to run but none was provided.

intermediate

How can you check if a block was given before calling yield?

Use the method block_given? which returns true if a block is passed, otherwise false.

beginner

Write a simple Ruby method that uses yield to run a block.

def greet
  puts "Hello"
  yield
  puts "Goodbye"
end

greet { puts "Nice to meet you!" }

What does yield do inside a Ruby method?

A Raises an error always

B Returns the method immediately

C Defines a new block

D Runs the block passed to the method

yield runs the block given to the method at that point.

How do you write a block when calling a method in Ruby?

A Using <code>{ ... }</code> or <code>do ... end</code> after the method call

B Inside parentheses after the method name

C Using square brackets <code>[ ... ]</code>

D Blocks are not allowed in Ruby

Blocks are written after the method call using curly braces or do-end.

What method checks if a block was given to a Ruby method?

A yield?

B block_given?

C has_block?

D block?

block_given? returns true if a block was passed.

What error occurs if yield is called without a block?

A SyntaxError

B NoMethodError

C LocalJumpError

D ArgumentError

Ruby raises LocalJumpError when yield has no block.

Which is a correct way to use yield in a method?

A def example; yield; end

B def example; yield?; end

C def example; yield(); end

D def example; yield block; end

yield is called simply as yield inside the method.

Explain how yield works in Ruby methods and why it is useful.

Think about how a method can run extra code given from outside.

Describe how to safely use yield when a block might not be given.

How to prevent errors if no block is passed?