Blocks

Blocks in Ruby

A block is a chunk of code you pass to a method, written between { } or do...end:

[1, 2, 3].each { |n| puts n }

[1, 2, 3].each do |n|
  puts n
end

Both forms are equivalent. Convention: use { } for one-liners, do...end for multi-line.

yield

Inside a method, use yield to call the block that was passed:

def run_twice
  yield
  yield
end

run_twice { puts "hello" }
# hello
# hello

block_given?

Check if a block was provided before yielding:

def maybe_run
  if block_given?
    yield
  else
    puts "no block"
  end
end

Passing Values to the Block

yield can pass arguments to the block:

def repeat(n)
  n.times { |i| yield i }
end

repeat(3) { |i| puts "step #{i}" }
# step 0
# step 1
# step 2

Your Task

Write a method apply_twice that calls the block twice using yield.

Then call it with a block that puts "Hello!".