list_building.rb

# original code 

# we have an array of strings
#
# we want to build a HTML list, where each string is wrapped in a <li> tag
# <li>s are separated by <hr>s
#
# conventional way: build the result string piece by piece:
#
# starting with the opening <ul> tag
# looping over the strings and adding the <li>s, and a <hr> UNLESS we are dealing with the last <li>
# finally, closing the <ul> tag

def apps_list
  apps = App.where.not(name: @current_app.name).all_valid.pluck(:name)

  ul_content = "<ul class='list-unstyled list-popover apps-selector'>"

  apps.each_with_index do |app, index|
    ul_content += wrap_with_li app
    ul_content += '<hr>' unless last_item?(index, apps.size)
  end

  ul_content + '</ul>'
end

# refactored code
# using Array#map to wrap `app`s in <li> tags
# then joining the <li> tags with <hr>
# finally tossing the above result into an <ul> sandwich

 def apps_list
   apps = App.where.not(name: @current_app.name).all_valid.pluck(:name)

   list_items = apps.map { |app| wrap_with_li app }.join('<hr>')

   <<-LIST
     <ul class='list-unstyled list-popover apps-selector'>
       #{list_items}
     </ul>
   LIST
end

# drop temporary variable
# even though shorter, it's a bit too code golf-y 💻🏌⛳️ for my tastes
# I think explicitly naming list_items is worth the extra clarity
# so I slightly prefer the first pass, although this is not too bad either

def apps_list
  apps = App.where.not(name: @current_app.name).all_valid.pluck(:name)

  <<-LIST
    <ul class='list-unstyled list-popover apps-selector'>
      #{ apps.map { |app| wrap_with_li app }.join('<hr>') }
    </ul>
  LIST
end