block.rb

puts "block - yield ========================================================="
class FtpManager
  def upload_file(file_path='file1')
    open_connection do |connection|
      puts "do something with #{connection}"
    end
  end

  def remove_file(file_path='file')
    open_connection do |connection|
      puts "do something with #{connection}"
    end
  end

  private

  def open_connection
    puts "open connection"
    yield('<connection_object>')
    puts "close connection / handle errors if raised"
  end
end

puts ":: call remove_file"
FtpManager.new.remove_file

puts "block - yield - optional =============================================="

class FtpManager2
  def upload_file(file_path='file1')
    open_connection do |connection|
      puts "do something with #{connection}"
    end
  end

  def remove_file(file_path='file')
    open_connection do |connection|
      puts "do something with #{connection}"
    end
  end

  def open_connection
    puts "open connection"
    if block_given?
      yield('<connection_object>')
      puts "close connection / handle errors if raised"
    else
      '<connection_object>'
    end
  end
end

puts ":: call remove_file"
FtpManager2.new.remove_file
puts ":: call open_connection"
puts FtpManager2.new.open_connection

puts "block - call =========================================================="

class FtpManager3
  def upload_file(file_path='file1')
    open_connection do |connection|
      puts "do something with #{connection}"
    end
  end

  def remove_file(file_path='file')
    open_connection do |connection|
      puts "do something with #{connection}"
    end
  end

  private

  def open_connection(&block)
    puts "open connection"
    block.call('<connection_object>')
    puts "close connection / handle errors if raised"
  end
end

puts ":: call remove_file"
FtpManager3.new.remove_file

Other example:

def wrap_in_h1
  "<h1>#{yield}</h1>"
end

wrap_in_h1 { "Here's my heading" }

# => "<h1>Here's my heading</h1>"

There is no functional difference between yield and block.call. Some developers prefer the more explicit style with block.call.

We can pass block of code to any method but it will be executed only if it calls yield or block.call
When we pass something other that block of code, it will try to execute on it method to_proc.

That's why this shortcut works:

puts ['ala', 'ma', 'kota'].map { |word| word.capitalize }.join(" ")
puts ['ala', 'ma', 'kota'].map(&:capitalize).join(" ")

It works because Symbol implements #to_proc method which returns block to #map that can be executed