How to Pass Proc to Method in Ruby: Simple Guide

In Ruby, you can pass a Proc object to a method by using the & symbol before the proc parameter in the method definition. When calling the method, pass the proc as an argument with & to convert it into a block.

Syntax

To pass a proc to a method, define the method with a parameter prefixed by &. This tells Ruby to convert the proc into a block inside the method. When calling the method, pass the proc with & to convert it back into a block.

• def method_name(&block): method accepts a proc as a block
• method_name(&proc_variable): pass proc as block

ruby

def example_method(&block)
  block.call
end

my_proc = Proc.new { puts "Hello from proc!" }
example_method(&my_proc)

Output

Hello from proc!

Example

This example shows how to define a method that takes a proc and calls it. The proc is created separately and passed to the method using &. The method then runs the proc's code.

ruby

def greet(&block)
  puts "Before proc call"
  block.call("Ruby")
  puts "After proc call"
end

say_hello = Proc.new { |name| puts "Hello, #{name}!" }
greet(&say_hello)

Output

Before proc call
Hello, Ruby!
After proc call

Common Pitfalls

Common mistakes include forgetting the & when passing the proc to the method or when defining the method parameter. Without &, Ruby treats the proc as a normal argument, not a block, causing errors when calling block.call.

Also, passing a block directly without converting it to a proc when needed can cause confusion.

ruby

def wrong_method(block)
  block.call
end

my_proc = Proc.new { puts "Hi!" }

# This will cause an error because block is not a proc but a normal argument
# wrong_method(my_proc) #=> NoMethodError

# Correct way:
def right_method(&block)
  block.call
end
right_method(&my_proc)

Quick Reference

Action	Syntax	Description
Define method to accept proc	def method_name(&block)	Method receives proc as block parameter
Pass proc to method	method_name(&proc_variable)	Convert proc to block when calling
Call proc inside method	block.call	Execute the proc's code
Create proc	my_proc = Proc.new { ... }	Define a proc object

Key Takeaways

Use & before a parameter in method definition to accept a proc as a block.

Pass a proc to a method by prefixing it with & to convert it into a block.

Inside the method, call the proc using block.call to run its code.

Forgetting & when passing or receiving procs causes errors.

Procs allow flexible code blocks to be passed around and reused.