# yield calls a passed block (anonymous function) passed to the method

​

def some_method

  puts "Before caling the block"

  yield

  puts "After calling the block"

end

​

# if a method yields and there was no block

# an error is raised

some_method #=> no block given (yield) (LocalJumpError)

​

# Here is a shortened syntax of passing a block

some_method { puts "Hello from the block" } 

#=> Before caling the block

#=> Hello from the block

#=> After caling the block

​

# Here is the longer syntax of passing a block

some_method do

  puts "Hello from the block"

end

​

# You can use the `block_given?` method to

# determine whether a block is present

def method_with_optional_block

  puts "Before caling the block"

  yield if block_given?

  puts "After calling the block"

end

​

# No error is raised when no block has been passed

method_with_optional_block

#=> Before caling the block

#=> After caling the block

​

method_with_optional_block { puts "Hello" }

#=> Before caling the block

#=> Hello

#=> After caling the block

​

# You can also capture the block as a `Proc`

def method_with_proc_block(&block)

  # same thing as `yield if block_given?`

  block.call if block

  # You can forward the passed block to another method

  some_method(&block)

end  

module CustomEnumerable

    def my_each ()

        # your code here!

        for i in 0...self.length

            yield(self[i])

        end

    end

end

class Array

    include CustomEnumerable

end

​

[1,2,3,4].my_each { |i| puts i } # => 1 2 3 4

[1,2,3,4].my_each { |i| puts i * 10 } # => 10 20 30 40