How to Pass Block to Method in Ruby: Simple Guide

In Ruby, you can pass a block to a method by defining the method normally and then calling it with a block using yield inside the method. Alternatively, you can capture the block as a parameter using &block and call it with block.call.

Syntax

To pass a block to a method, you write the method normally and use yield to execute the block inside the method. You can also accept the block as a parameter using &block and call it with block.call.

• yield: Runs the block passed to the method.
• &block: Captures the block as a Proc object.
• block.call: Executes the captured block.

ruby

def greet
  puts "Hello"
  yield if block_given?
  puts "Goodbye"
end

Example

This example shows a method greet that takes a block and runs it between two print statements. It demonstrates both yield and &block usage.

ruby

def greet
  puts "Hello"
  yield if block_given?
  puts "Goodbye"
end

greet do
  puts "Nice to meet you!"
end

# Using &block

def greet_with_block(&block)
  puts "Hello"
  block.call if block
  puts "Goodbye"
end

greet_with_block do
  puts "Nice to meet you again!"
end

Output

Hello
Nice to meet you!
Goodbye
Hello
Nice to meet you again!
Goodbye

Common Pitfalls

Common mistakes include forgetting to check if a block is given before calling yield, which causes an error if no block is passed. Also, confusing yield and &block usage can lead to unexpected behavior.

Always use block_given? before yield or check if block is not nil before calling block.call.

ruby

def wrong_method
  yield
end

# Calling without block causes error:
# wrong_method

# Correct way:
def safe_method
  yield if block_given?
end

safe_method do
  puts "Block runs safely"
end

Output

Block runs safely

Quick Reference

Concept	Description	Example
Passing block with yield	Runs the block inside method	yield if block_given?
Capturing block as parameter	Receives block as Proc object	def method(&block)
Calling captured block	Executes the block object	block.call if block
Check block presence	Avoid errors if no block	block_given? or block != nil

Key Takeaways

Use yield inside a method to run a passed block.

Use &block to capture the block as a parameter and call it with block.call.

Always check if a block is given with block_given? before calling yield.

For &block, check if the block is not nil before calling block.call.

Passing blocks makes methods flexible and allows custom code execution inside them.