Writing a Method that Accepts a Block in Ruby

Introduction

Ruby is a general-purpose, dynamic, reflective, object-oriented programming language. Everything in Ruby is an object. Ruby's development aimed to create a user interface between human programmers and the underlying computational machinery.

As there are closures in different programming languages, Ruby have blocks. A block in Ruby is similar to a method but does not belong to an object.

Let’s learn how to write a method that accepts a block in Ruby.

How to Write a Method that Accepts a Block?

You need to do nothing specific to enable your method to accept a block. If the caller passes one in, any method can use it. You may call the block with the yield keyword at any point in your method.

Let’s understand the above statement with examples.

Example 1:

# Ruby program to show a method accepting block using yield statement

# method
def ninjas

	# method statement to be executed
	puts "Ninjas are Coders!"

	# using yield statement
	yield

	# method statement to be executed
	puts "Ninjas are Developers!"

	# using yield statement
	yield
	
end

# block
ninjas{puts "Ninjas are Data Scientists!"}

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Output:

In the above program, the method name is ninjas. Method statements are initially invoked, demonstrating that Ninjas are Coders!. However, as soon as yield statements are executed, control is transferred to the block, which then executes its own statements, demonstrating that Ninjas are Data Scientists!. When the Block completes, it returns control to the method, which then continues to run from where the yield statement was invoked. 

Example 2:

# Ruby program to show a method accepting block using yield statement

# method
def func(n)
    
    # if block is provided
	if block_given?
    	n.times { yield }

	# if block is not provided
	else
		raise ArgumentError.new("Error! Block is not provided.")
 
	end
end

# block
func(5) { puts "Coding Ninjas!" }

# block is not provided
func(5)

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Output:

In the above program, the method name is func. We are invoking the method two times, one with the block argument and another without argument. When we provide the argument, it gives the output as Coding Ninjas! Five times. And when the argument is not provided, it will go in the else statement and shows the Error message Error! Block is not provided.

Providing Arguments to Yield Statement

You can provide arguments to yield (which will be given to the block) and act upon the yield statement's value (this is the value of the last statement in the block).

Here is an example of a method that uses the value of the code block and accepts parameters for its block:-

# Ruby program to show a method that uses the value of the code block and accepts parameters for its block.

# method
def ninjas
    
	var1 = yield("Coders")
	puts "Ninjas are best #{var1}!"

	var2 = yield("Developers")
	puts "Ninjas are best #{var2}!"
    
end

# block
ninjas do |designation|
    puts "Ninjas are #{designation}!"
    designation == "Coders" ? "Coders in the World" : "Developers in the World"
end

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Output:

In the above program, we can see that we are passing an argument to the yield statement and that arguments we can again use as a variable to execute the method statement.