Using blocks with yield

Notes on the Le Wagon Iteratros & Blocks About Blocks exercise

Intoduction to blocks and using yield.


Yield is a Ruby keyword executing the block. It tells the method to execute a block now.

Lets start with a timer method which will simply return the time taken to execute a given block.

def timer_for
  start_time =
  end_time =
  time_taken = end_time - start_time
  return time_taken
  1. We start by setting start_time to the current time by using

  2. Use the keyword ‘Yield’ to tell the method to run the block now

  3. Set end_time to

  4. Assign the calculation of end_time - start_time to time_taken and return it to get the total time taken.

Achieving .map behaviour without using .map

def my_map(array)
  new_array = []
  array.each do |name|
    new_array << yield(name)
  return new_array

‘.map’ will create a new array for us. However, if we are not using .map then we must create this new array ourselves by setting new_array to an empty array.

We then iterate over the array with .each. We can then use yield to call the block this time giving it a parameter so that it will call the block and insert the parameter of name.

You can then return the new array.

Building HTML tags around content in a block

def tag(tag_name, attributes = nil)
  attr_name = attributes.nil? ? nil : attributes.first
  attr_value = attributes.nil? ? nil : attributes.last

  open_tag = attributes.nil? ? tag_name : "#{tag_name} #{attr_name}=\"#{attr_value}\""
  content = yield

This method takes two parameters tag_name and attributes. = nil means that if no parameter is given then it will assign it to nil. You can think of it as being an optionl parameter.

We start by calling nil? on atrributes to check if it is nil or if a parameter has been given. It returns a boolean value. We use a ternary operator which says if the value is true ( meaning it is nil) then keep it as nil otherwise grab the first element. The same logic is applied to attr_value but we take the last element instead.

Then we define an open_tag which also makes use of a ternary operator. It states that if the attribute is nil then return the tag_name only but if not then build the following:

"#{tag_name} #{attr_name}=\"#{attr_value}\""

We have interploated the tag name and then the attirbute (for example “style”). Then we have an = and an interpolation of the attibute value (for example “color: red”). We require the use of the \ in order to use " in the middle of the string. It just means it ignores the character and does not treat it as the end of the string.

Then we say that content is = to running the block (yield). Finally we build our HTML code.


We interpoloate each part to make the HTML code, adding in essential characters where needed.This is returned as a string.